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Encyclopedia > Genetics

Genetics, a discipline of biology, is the science of heredity and variation in living organisms.[1][2] The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the process of inheritance, only began with the work of Gregor Mendel in the mid-nineteenth century.[3] Although he did not know the physical basis for heredity, Mendel observed that organisms inherit traits in a discrete manner—these basic units of inheritance are now called genes. Pork and beans (not to be confused with the Journal of Genetics) is a yearly scientific journal publishing investigations bearing on heredity and variation. ... Animation of a section of DNA rotating. ... For the song by Girls Aloud see Biology (song) Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: Βιολογία - βίος, bio, life; and λόγος, logos, speech lit. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... The ancients had a variety of ideas about heredity: Theophrastus proposed that male flowers caused female flowers to ripen; Hippocrates speculated that seeds were produced by various body parts and transmitted to offspring at the time of conception, and Aristotle thought that male and female semen mixed at conception. ... Genetic variation is the variation in the genetic material of a population, and includes the nuclear, mitochodrial, ribosomal genomes as well as the genomes of other organelles. ... Domains and Kingdoms Nanobes Acytota Cytota Bacteria Neomura Archaea Eukaryota Bikonta Apusozoa Rhizaria Excavata Archaeplastida Rhodophyta Glaucophyta Plantae Heterokontophyta Haptophyta Cryptophyta Alveolata Unikonta Amoebozoa Opisthokonta Choanozoa Fungi Animalia An ericoid mycorrhizal fungus Life on Earth redirects here. ... Prehistory (Greek words προ = before and ιστορία = history) is the period of human history prior to the advent of writing (which marks the beginning of recorded history). ... Selective breeding in domesticated animals is the process of developing a cultivated breed over time. ... “Mendel” redirects here. ... In mathematics, a countable set is a set with the same cardinality (i. ... For other uses, see Gene (disambiguation). ...

DNA, the molecular basis for inheritance. Each strand of DNA is a chain of nucleotides, matching each other in the center to form what look like rungs on a twisted ladder.
DNA, the molecular basis for inheritance. Each strand of DNA is a chain of nucleotides, matching each other in the center to form what look like rungs on a twisted ladder.

Genes correspond to regions within DNA, a molecule composed of a chain of four different types of nucleotides—the sequence of these nucleotides is the genetic information organisms inherit. DNA naturally occurs in a double stranded form, with nucleotides on each strand complementary to each other. Each strand can act as a template for creating a new partner strand—this is the physical method for making copies of genes that can be inherited. The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... A nucleotide is an organic molecule consisting of a heterocyclic nucleobase (a purine or a pyrimidine), a pentose sugar (deoxyribose in DNA or ribose in RNA), and a phosphate or polyphosphate group. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... A nucleotide is an organic molecule consisting of a heterocyclic nucleobase (a purine or a pyrimidine), a pentose sugar (deoxyribose in DNA or ribose in RNA), and a phosphate or polyphosphate group. ... DNA replication. ...


The sequence of nucleotides in a gene is translated by cells to produce a chain of amino acids, creating proteins—the order of amino acids in a protein corresponds to the order of nucleotides in the gene. This is known as the genetic code. The amino acids in a protein determine how it folds into a three-dimensional shape; this structure is, in turn, responsible for the protein's function. Proteins carry out almost all the functions needed for cells to live. A change to the DNA in a gene can change a protein's amino acids, changing its shape and function: this can have a dramatic effect in the cell and on the organism as a whole. Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... This article is about the class of chemicals. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... For a non-technical introduction to the topic, see Introduction to Genetics. ...


Although genetics plays a large role in the appearance and behavior of organisms, it is the combination of genetics with what an organism experiences that determines the ultimate outcome. For example, while genes play a role in determining a person's height, the nutrition and health that person experiences in childhood also have a large effect. Stature redirects here. ... The Nutrition Facts table indicates the amounts of nutrients which experts recommend you limit or consume in adequate amounts. ...

Contents

History

Main article: History of genetics
Morgan's observation of sex-linked inheritance of a mutation causing white eyes in Drosophila led him to the hypothesis that genes are located upon chromosomes.
Morgan's observation of sex-linked inheritance of a mutation causing white eyes in Drosophila led him to the hypothesis that genes are located upon chromosomes.

Although the science of genetics began with the work of Gregor Mendel in the mid-1800's, there were some theories of inheritance that preceded Mendel. A popular theory during Mendel's time was the concept of blending inheritance: the idea that individuals inherit a smooth blend of traits from their parents. Mendel's work disproved this, showing that traits are composed of combinations of distinct genes rather than a continuous blend. Also popular at the time was the theory of inheritance of acquired characteristics: the belief that individuals inherit traits that have been strengthened in their parents. This theory (commonly associated with Jean-Baptiste Lamarck) is now known to be wrong, the experiences of individuals do not affect the genes they pass to their children.[4] Gregor Mendel, the father of genetics The history of genetics is generally held to have started in 1865 when an Austrian monk, Gregor Mendel published his work on pea plants. ... Image File history File links Sexlinked_inheritance_white. ... Image File history File links Sexlinked_inheritance_white. ... Type species Drosophila funebris (Fabricius, 1787) Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called fruit flies, or more appropriately vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies, a reference to the characteristic of many species to linger... “Mendel” redirects here. ... Gregor Johann Mendel In Darwins time, biologists held to the theory of blending inheritance -- an offspring was an average of its parents. ... The inheritance of acquired characters (or characteristics) is the hereditary mechanism by which changes in physiology acquired over the life of an organism (such as muscle enlarged through use) are transmitted to offspring. ... Portrait of Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (August 1, 1744 – December 18, 1829) was a French soldier, naturalist, academic and an early proponent of the idea that evolution occurred and proceeded in accordance with natural laws. ...


Mendelian and classical genetics

The modern science of genetics traces its roots to Gregor Johann Mendel, a German-Czech Augustinian monk and scientist who studied of the nature of inheritance in plants. In his paper "Versuche über Pflanzenhybriden" ("Experiments on Plant Hybridization"), presented in 1865 to the Brunn Natural History Society, Gregor Mendel traced the inheritance patterns of certain traits in pea plants and showed that they could be described mathematically.[5] Although this pattern of inheritance could only be observed for a few traits, Mendel's work suggested that statistics was a useful tool for studying inheritance. Gregor Johann Mendel (July 22, 1822 – January 6, 1884) was an Austrian monk who is often called the father of genetics for his study of the inheritance of traits in pea plants. ... The Augustinians, named after Saint Augustine of Hippo (died AD 430), are several Roman Catholic monastic orders and congregations of both men and women living according to a guide to religious life known as the Rule of Saint Augustine. ... For other uses, see Monk (disambiguation). ... Written in 1865 by Gregor Mendel, Experiments on Plant Hybridization (German: Versuche über Pflanzen-Hybriden) was the result after years spent studying genetic traits in pea plants. ... “Mendel” redirects here. ...


The importance of Mendel's work was not understood until early in the 1900's, after his death, when his research was re-discovered by other scientists working on similar problems. The word genetics itself was coined in 1905 by William Bateson, a proponent of Mendel's work, in a letter to Adam Sedgwick.[6][7] (The adjective genetic, derived from the Greek word genno (γεννώ): to give birth, predates the noun and was first used in a biological sense in 1860.[8]) Bateson popularized the usage of the word genetics to describe the study of inheritance in his inaugural address to the Third International Conference on Plant Hybridization in London, England, in 1906.[9] William Bateson. ... Adam Sedgwick (March 22nd, 1785–January 27, 1873) was one of the founders of modern geology. ...


After the rediscovery of Mendel's work, scientists tried to discover which molecules in the cell were responsible for inheritance. In 1910 Thomas Hunt Morgan argued that genes are on chromosomes, based on observations of a sex-linked white eye mutation in fruit flies.[10] In 1913 his student Alfred Sturtevant used the phenomenon of genetic linkage to show that genes are arranged linearly on the chromosome.[11] Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) was an American geneticist and embryologist. ... Alfred Henry Sturtevant (November 21, 1891–April 5, 1970) was an American geneticist, Sturtevant constructed the first genetic map of a chromosome in 1913. ... Genetic linkage occurs when particular alleles are inherited jointly. ...

James D. Watson (pictured) and Francis Crick resolved the structure of DNA in 1953.
James D. Watson (pictured) and Francis Crick resolved the structure of DNA in 1953.

Image File history File links Download high-resolution version (963x1200, 119 KB) James D. Watson, source: http://www. ... Image File history File links Download high-resolution version (963x1200, 119 KB) James D. Watson, source: http://www. ... For other people named James Watson, see James Watson (disambiguation). ... Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004), (Ph. ...

Molecular genetics

Although genes were known to exist on chromosomes, chromosomes are composed of both protein and DNA: scientists didn't know which of these was responsible for inheritance. In 1928, Frederick Griffith discovered of the phenomenon of transformation (see Griffith's experiment): dead bacteria could transfer genetic material to "transform" other still-living bacteria. Sixteen years later, in 1944, Oswald Theodore Avery, Colin McLeod and Maclyn McCarty identified the molecule responsible for transformation as DNA.[12] The Hershey-Chase experiment in 1952 also showed that DNA (rather than protein) was the genetic material of the viruses that infect bacteria, further evidence that DNA was the molecule responsible for inheritance.[13] Frederick Griffith (1879 - 1941) was a British medical officer. ... It has been suggested that this article or section be merged into Transfection. ... Griffiths experiment discovering the transforming principle in pneumococcus bacteria. ... Oswald Avery in 1937 Oswald Theodore Avery ( 1877- 1955) was a physician, medical researcher and early molecular biologist. ... Colin Monroe McLeod (1909 – 1972) was a Canadian-American geneticist. ... Maclyn McCarty (June 9, 1911–January 2, 2005) was an American geneticist. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... The Hershey-Chase experiment was a series of experiments conducted in 1952 by Alfred Hershey and Martha Chase. ...


James D. Watson and Francis Crick solved the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin that indicated DNA had a helical structure (ie. shaped like a corkscrew).[14][15] Their double-helix model had two strands of DNA with the nucleotides pointing inwards, each matching a complementary nucleotide on the other strand to form what looks like rungs on a twisted ladder.[16] This structure showed that genetic information exists in the sequence of nucleotides on each strand of DNA. The structure also suggested a simple method for duplication: if the strands are separated, new partner strands can be reconstructed for each based on the sequence of the old strand. For other people named James Watson, see James Watson (disambiguation). ... Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004), (Ph. ... X-ray crystallography, also known as single-crystal X-ray diffraction, is the oldest and most common crystallographic method for determining the structure of molecules. ... Rosalind Elsie Franklin (25 July 1920 Kensington, London – 16 April 1958 Chelsea, London) was an English biophysicist and X-ray crystallographer who made important contributions to the understanding of the fine structures of DNA, viruses, coal and graphite. ... This article is about the shape. ...


Although the structure of DNA showed how inheritance worked, it was still not known how DNA influenced the behavior of cells. In the following years scientists tried to understand how DNA controls the process of protein production. It was discovered that the cell uses DNA as a template to create matching messenger RNA (a molecule with nucleotides, very similar to DNA). The nucleotide sequence of a messenger RNA is used to create an amino acid sequence in protein; this translation between nucleotide and amino acid sequences is known as the genetic code. A representation of the 3D structure of myoglobin showing coloured alpha helices. ... The life cycle of an mRNA in a eukaryotic cell. ... This article is about the class of chemicals. ... For a non-technical introduction to the topic, see Introduction to Genetics. ...


With this molecular understanding of inheritance, an explosion of research became possible. One important development was chain-termination DNA sequencing in 1977 by Frederick Sanger: this technology allows scientists to read the nucleotide sequence of a DNA molecule.[17] In 1983 the polymerase chain reaction was developed by Kary Banks Mullis, providing an quick way to isolate and amplify a specific section of a DNA from a mixture.[18] These and other techniques, through the pooled efforts of the Human Genome Project and parallel private effort by Celera Genomics, culminated in the sequencing of the human genome in 2003.[19] The term DNA sequencing encompasses biochemical methods for determining the order of the nucleotide bases, adenine, guanine, cytosine, and thymine, in a DNA oligonucleotide. ... Frederick Sanger, OM, CH, CBE, FRS (born 13 August 1918) is an English biochemist and a two time Nobel laureate in chemistry. ... “PCR” redirects here. ... Kary Banks Mullis (born December 28, 1944) is a biochemist. ... The Human Genome Project (HGP) is an international scientific research project. ... Celera Genomics (NYSE: CRA) is a business unit of the Applera Corporation that focuses on genetic sequencing and related technologies. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...


Features of inheritance

Discrete inheritance and Mendel's laws

Main article: Mendelian inheritance
A Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms
A Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms

At its most fundamental level, inheritance in organisms occurs by means of discrete traits, called genes.[20] This property was first observed by Gregor Mendel, who studied the segregation of heritable traits in pea plants.[5][21] In his experiments studying the trait for flower color, Mendel observed that the flowers of each pea plant were either purple or white—and never an intermediate between the two colors. These different, discrete versions of the same gene are called alleles. Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... For other uses, see Gene (disambiguation). ... “Mendel” redirects here. ... Binomial name L. Percentages are relative to US recommendations for adults. ... An allele (pronounced , ) (from the Greek αλληλος, meaning each other) is one member of a pair or series of different forms of a gene. ...


In the case of pea plants, each organism has two alleles of each gene, and the plants inherit one allele from each parent.[22] Many organisms, including humans, have this pattern of inheritance. Organisms with two copies of the same allele are called homozygous, while organisms with two different alleles are heterozygous. Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ... Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. ...


The set of alleles for a given organism is called its genotype, while the observable trait the organism has is called its phenotype. When organisms are heterozygous, often one allele is called dominant as its qualities dominate the phenotype of the organism, while the other allele is called recessive as its qualities recede and are not observed. Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype, or codominance by expressing both alleles at once.[23] This article does not cite any references or sources. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... In genetics, dominant allele refers to a genetic feature that hides the recessive allele. ... In genetics, the term recessive gene refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in a homozygous genotype (an organism that has two copies of the same allele). ... In genetics, dominance describes a specific relationship between the effects of different versions of a gene (alleles) on a trait (phenotype). ... In genetics, dominance describes a specific relationship between the effects of different versions of a gene (alleles) on a trait (phenotype). ...


When a pair of organisms reproduce sexually, their offspring randomly inherit one of the two alleles from each parent. These observations of discrete inheritance and the segregation of alleles are collectively known as Mendel's first law or the Law of Segregation. Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. ...

Genetic pedigree charts help track the inheritance patterns of traits.
Genetic pedigree charts help track the inheritance patterns of traits.

Notation and diagrams

Geneticists use diagrams and symbols to describe inheritance. A gene is represented by a letter (or letters)—the capitalized letter represents the dominant allele and the recessive is represented by lowercase.[24] Often a "+" symbol is used to mark the usual, non-mutant allele for a gene.


In fertilization and breeding experiments (and especially when discussing Mendel's) the parents are referred to as the "P" generation and the offspring as the "F1" (first filial) generation. When the F1 offspring mate with each other, the offspring are called the "F2" (second filial) generation. One of the common diagrams used to predict the result of cross-breeding is the Punnett square. The Punnett square is a diagram designed by Reginald Punnett and used by biologists to determine the probability of an offspring having a particular genotype. ...


When studying human genetic diseases, geneticists often use pedigree charts to represent the inheritance of traits.[25] These charts map the inheritance of a trait in a family tree. A pedigree chart is a chart which tells one all of the known phenotypes for an organism and its ancestors, most commonly humans, show dogs, and race horses. ...


Interactions of multiple genes

Human height is a complex genetic trait. Francis Galton's data from 1889 shows the relationship between offspring height as a function of mean parent height. While correlated, remaining variation in offspring heights indicates environment is also an important factor in this trait.
Human height is a complex genetic trait. Francis Galton's data from 1889 shows the relationship between offspring height as a function of mean parent height. While correlated, remaining variation in offspring heights indicates environment is also an important factor in this trait.

Organisms have thousands of genes, and in sexually reproducing organisms assortment of these genes are generally independent of each other. This means that the inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers. This phenomenon, known as "Mendel's second law" or the "Law of independent assortment", means that the alleles of different genes get shuffled between parents to form offspring with many different combinations. (Some genes do not assort independently, demonstrating genetic linkage, a topic discussed later in this article.) This article does not cite any references or sources. ... Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. ... Genetic linkage occurs when particular alleles are inherited jointly. ...


Often different genes can interact in a way that influences the same trait. In the Blue-eyed Mary (Omphalodes verna), for example, there exists a gene with alleles that determine the color of flowers: blue or magenta. Another gene, however, controls whether the flowers have color at all: color or white. When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles. This interaction between genes is called epistasis, with the second gene epistatic to the first.[26] Binomial name Omphalodes verna Moench The Blue-eyed Mary or Navelwort (Omphalodes verna) is a perennial plant native to Central and South-east Europe. ... Epistasis takes place when the action of one gene is modified by one or more others that assort somewhat independently. ...


Many traits are not discrete features (eg. purple or white flowers) but are instead continuous features (eg. human height and skin color). These complex traits are the product of many genes.[27] The influence of these genes is mediated, to varying degrees, by the environment an organism has experienced. The degree to which an organism's genes contribute to a complex trait is called heritability.[28] Measurement of the heritability of a trait is relative—in a more variable environment, the environment has a bigger influence on the total variation of the trait. For example, human height is a complex trait with a heritability of 89% in the United States. In Nigeria, however, where people experience a more variable access to good nutrition and health care, height has a heritability of only 62%.[29] Inheritance of quantitative traits refers to the inheritance of a phenotypic characteristic that varies in degree and can be attributed to the interactions between two or more genes and their environment (also called Polygenic inheritance). ... In genetics, heritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. ...


Molecular basis for inheritance

DNA and chromosomes

Main articles: DNA and Chromosome
The molecular structure of DNA. Bases pair through the arrangement of hydrogen bonding between the strands.
The molecular structure of DNA. Bases pair through the arrangement of hydrogen bonding between the strands.

The molecular basis for genes is deoxyribonucleic acid (DNA). DNA is composed of a chain of nucleotides, of which there are four types: adenine (A), cytosine (C), guanine (G), and thymine (T). Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain.[30] Viruses are the only exception to this rule—sometimes viruses use the very similar molecule RNA instead of DNA as their genetic material.[31] The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... For information about chromosomes in genetic algorithms, see chromosome (genetic algorithm). ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Geometry of the water molecule Molecules have fixed equilibrium geometries--bond lengths and angles--that are dictated by the laws of quantum mechanics. ... In chemistry, a hydrogen bond is a type of attractive intermolecular force that exists between two partial electric charges of opposite polarity. ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... DNA replication Deoxyribonucleic acid (DNA) is a nucleic acid which carries genetic instructions for the biological development of all cellular forms of life and many viruses. ... A nucleotide is an organic molecule consisting of a heterocyclic nucleobase (a purine or a pyrimidine), a pentose sugar (deoxyribose in DNA or ribose in RNA), and a phosphate or polyphosphate group. ... For the programming language Adenine, see Adenine (programming language). ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA; the others being adenine, cytosine, thymine, and uracil. ... For the similarly-spelled vitamin compound, see Thiamine Thymine, also known as 5-methyluracil, is a pyrimidine nucleobase. ... This article is about biological infectious particles. ... For other uses, see RNA (disambiguation). ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ...


DNA normally exists as a double-stranded molecule, coiled into the shape of a double-helix. Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand: A pairs with T, and C pairs with G. Thus, in its two-stranded form, each strand effectively contains all necessary information, redundant with its partner strand. This structure of DNA is the physical basis for inheritance: DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand.[32] A staircase in the shape of a double helix, in the Vatican Museum Image of a DNA chain which shows the double helix replicating itself In geometry a double helix (plural helices) typically consists of two congruent helices with the same axis, differing by a translation along the axis, which... DNA replication. ...


Genes are arranged linearly along long chains of DNA sequence, called chromosomes. In bacteria, each cell has a single circular chromosome, while eukaryotic organisms (which includes plants and animals) have their DNA arranged in multiple linear chromosomes. These DNA strands are often extremely long; the largest human chromosome, for example, is about 247 million base pairs in length.[33] The DNA of a chromosome is associated with structural proteins that organize, compact, and control access to the DNA, forming a material called chromatin; in eukaryotes chromatin is usually composed of nucleosomes, repeating units of DNA wound around a core of histone proteins.[34] The full set of hereditary material in an organism (usually the combined DNA sequences of all chromosomes) is called the genome. This article is about the biological chromosome. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Base pairs, of a DNA molecule. ... Chromatin is the complex of DNA and protein found inside the nuclei of eukaryotic cells. ... Chromatin is the complex of DNA and protein found inside the nuclei of eukaryotic cells. ... A nucleosome is a unit made of DNA and histones. ... Schematic representation of the assembly of the core histones into the nucleosome. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...


While haploid organisms have only one copy of each chromosome, most animals and many plants are diploid, containing two of each chromosome and thus two copies of every gene.[35] The two alleles for a gene are located on identical loci of sister chromatids, each allele inherited from a different parent. Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... Short and long arms Chromosome. ... A chromatid forms one part of a chromosome after it has coalesced for the process of mitosis or meiosis. ...

Walther Flemming's 1882 diagram of eukaryotic cell division. Chromosomes are copied, condensed, and organized. Then, as the cell divides, chromosome copies separate into the daughter cells.
Walther Flemming's 1882 diagram of eukaryotic cell division. Chromosomes are copied, condensed, and organized. Then, as the cell divides, chromosome copies separate into the daughter cells.

An exception exists in the sex chromosomes, specialized chromosomes many animals have evolved that play a role in determining the sex of an organism.[36] In humans and other mammals the Y chromosome has very few genes and triggers the development of male sexual characteristics, while the X chromosome is similar to the other chromosomes and contains many genes unrelated to sex determination. Females have two copies of the X chromosome, but males have one Y and only one X chromosome—this difference in X chromosome copy numbers leads to the unusual inheritance patterns of sex linked disorders. Image File history File links Zell-substanz-book-illustrations. ... Image File history File links Zell-substanz-book-illustrations. ... Illustrations of cells with chromosomes and mitosis, from the book Zell-substanz, Kern und Zelltheilung, 1882 Walther Flemming (born April 21, 1843 in Sachsenberg, Germany; died August 4, 1905 in Kiel) was a founder of the study of cytogenetics. ... A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. ... Sex-linked genes are those carried on the mammalian X chromosome but not the Y chromosome. ...


Reproduction

When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis, is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from a single parent. Offspring that are genetically identical to their parents are called clones. It has been suggested that Parthenogenesis be merged into this article or section. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Mitosis divides genetic information during cell division. ... It has been suggested that Parthenogenesis be merged into this article or section. ... WGS-84 (GPS) Coordinates: , Statistics Province: Ulster County: Elevation: 71 m Population (2006)  - Town:  - Rural: 321 The word clones is also used as the plural of clone. ...


Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome (haploid) and double copies (diploid).[35] Haploid cells fuse and combine genetic material to create a diploid cell with paired chromosomes. Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes. Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes. Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ...


Although they do not use the haploid/diploid method of sexual reproduction, bacteria have many methods of acquiring new genetic information. Some bacteria can undergo conjugation, transferring a small circular piece of DNA to another bacterium.[37] Bacteria can also take up raw DNA fragments found in the environment and integrate them into their genome, a phenomenon known as transformation.[38] This processes result in horizontal gene transfer, transmitting fragments of genetic information between organisms that would otherwise be unrelated. Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. ... It has been suggested that this article or section be merged into Transfection. ... Horizontal gene transfer (HGT), also Lateral gene transfer (LGT), is any process in which an organism transfers genetic material to another cell that is not its offspring. ...

Thomas Hunt Morgan's 1916 illustration of a double crossover between chromosomes
Thomas Hunt Morgan's 1916 illustration of a double crossover between chromosomes

Image File history File links Size of this preview: 414 × 599 pixelsFull resolution (452 × 654 pixel, file size: 176 KB, MIME type: image/png) Cropped version of [[Image:Morgan_crossover_2. ... Image File history File links Size of this preview: 414 × 599 pixelsFull resolution (452 × 654 pixel, file size: 176 KB, MIME type: image/png) Cropped version of [[Image:Morgan_crossover_2. ... Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) was an American geneticist and embryologist. ...

Recombination and linkage

The diploid nature of chromosomes allows for genes on different chromosomes to assort independently during sexual reproduction, recombining to form new combinations of genes. Genes on the same chromosome would theoretically never recombine, however, were it not for the process of chromosomal crossover. During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes.[39] This process of chromosomal crossover generally occurs during meiosis, a series of cell divisions that creates haploid germ cells that later combine with other germ cells to form child organisms. Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... Genetic linkage occurs when particular alleles are inherited jointly. ... In genetics, Independent assortment is the process of random segregation and assortment of chromosomes during gametogenesis to produce genetically unique gametes. ... Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... For the figure of speech, see meiosis (figure of speech). ... Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ...


The probability of chromosomal crossover occurring between two given points on the chromosome is related to the distance between them. For an arbitrarily long distance, the probability of crossover is high enough that the inheritance of the genes is effectively uncorrelated. For genes that are closer together, however, the lower probability of crossover means that the genes demonstrate genetic linkage—alleles for the two genes tend to be inherited together. The amounts of linkage between a series of genes can be combined to form a linear linkage map that roughly describes the arrangement of the genes along the chromosome.[40] Genetic linkage occurs when particular alleles are inherited jointly. ... Genetic linkage occurs when particular alleles are inherited jointly. ...


Gene expression

The genetic code: DNA, through a messenger RNA intermediate, codes for protein with a triplet code.
The genetic code: DNA, through a messenger RNA intermediate, codes for protein with a triplet code.

Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... For a non-technical introduction to the topic, see Introduction to Genetics. ... The life cycle of an mRNA in a eukaryotic cell. ...

Genetic code

Main article: Genetic code

Genes generally express their functional effect through the production of proteins, which are complex molecules responsible for most functions in the cell. Proteins are chains of amino acids, and the DNA sequence of a gene (through an RNA intermediate) is used to produce a specific protein sequence. This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called transcription. For a non-technical introduction to the topic, see Introduction to Genetics. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... This article is about the class of chemicals. ... For other uses, see RNA (disambiguation). ... A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ...


This messenger RNA molecule is then used to produce a corresponding amino acid sequence through a process called translation. Each group of three nucleotides in the sequence, called a codon, corresponds to one of the twenty possible amino acids in protein—this correspondence is called the genetic code.[41] The flow of information is unidirectional: information is transferred from nucleotide sequences into the amino acid sequence of proteins, but never from protein back into the sequence of DNA—a phenomenon Francis Crick called the central dogma of molecular biology.[42] The life cycle of an mRNA in a eukaryotic cell. ... Translation is the second stage of protein biosynthesis (part of the overall process of gene expression). ... RNA codons. ... For a non-technical introduction to the topic, see Introduction to Genetics. ... Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004), (Ph. ... Information flow in biological systems The central dogma of molecular biology was first enunciated by Francis Crick in 1958[1] and re-stated in a Nature paper published in 1970:[2] POSTLEWAITE IS A TOOL The central dogma of molecular biology deals with the detailed residue-by-residue transfer of...

The dynamic structure of hemoglobin is responsible for its ability to transport oxygen within mammalian blood.
A single amino acid change causes hemoglobin to form fibers.
A single amino acid change causes hemoglobin to form fibers.

The specific sequence of amino acids results in a unique three-dimensional structure for that protein, and the three-dimensional structures of protein are related to their function.[43][44] Some are simple structural molecules, like the fibers formed by the protein collagen. Proteins can bind to other proteins and simple molecules, sometimes acting as enzymes by facilitating chemical reactions within the bound molecules (without changing the structure of the protein itself). Protein structure is dynamic; the protein hemoglobin bends into slightly different forms as it facilitates the capture, transport, and release of oxygen molecules within mammalian blood. Image File history File links Hb-animation2. ... Image File history File links Hb-animation2. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Protein before and after folding. ... Tropocollagen triple helix. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Structure of hemoglobin. ...


A single nucleotide difference within DNA can cause a single change in the amino acid sequence of a protein. Because protein structures are the result of their amino acid sequences, some changes can dramatically change the properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules. For example, sickle-cell anemia is a human genetic disease that results from a single base difference within the coding region for the β-globin section of hemoglobin, causing a single amino acid change that changes hemoglobin's physical properties.[45] Sickle-cell versions of hemoglobin stick to themselves, stacking to form fibers that distort the shape of red blood cells carrying the protein. These sickle-shaped cells no longer flow smoothly through blood vessels, having a tendency to clog or degrade, causing the medical problems associated with the disease. Sickle-shaped red blood cells Sickle-cell anemia or anaemia (also sickle-cell disease) is a genetic disorder in which red blood cells may change shape under certain circumstances. ...


Some genes are transcribed into RNA but are not translated into protein products—these are called non-coding RNA molecules. In some cases these products fold into structures which are involved in critical cell functions (eg. ribosomal RNA and transfer RNA). RNA can also have regulatory effect through hybridization interactions with other RNA molecules (eg. microRNA). A non-coding RNA (ncRNA) is any RNA molecule that is not translated into a protein. ... Ribosomal RNA (rRNA), a type of RNA synthesized in the nucleolus by RNA Pol I, is the central component of the ribosome, the protein manufacturing machinery of all living cells. ... Transfer RNA Transfer RNA (abbreviated tRNA), first hypothesized by Francis Crick, is a small RNA chain (73-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... The stem-loop secondary structure of a pre-microRNA from Brassica oleracea. ...


Nature vs. nurture

Although genes contain all the information an organism uses to function, the environment plays an important role in determining the ultimate phenotype—a dichotomy often referred to as "nature vs. nurture." The phenotype of an organism depends on the interaction of genetics with the environment. One example of this is the case of temperature-sensitive mutations. Often, a single amino acid change within the sequence of a protein does not change its behavior and interactions with other molecules, but it does destabilize the structure. In a high temperature environment, where molecules are moving more quickly and hitting each other, this results in the protein losing its structure and failing to function. In a low temperature environment, however, the protein's structure is stable and functions normally. This type of mutation is visible in the coat coloration of Siamese cats, where a mutation in an enzyme responsible for pigment production causes it to destabilize and lose function at high temperatures.[46] The protein remains functional in areas of skin that are colder—legs, ears, tail, and face—and so the cat has dark fur at its extremities. This article needs cleanup, so as to conform to a higher standard. ... For other uses, see Temperature (disambiguation). ... Irreversible egg protein denaturation and loss of solubility, caused by the high temperature (while cooking it) Denaturation is the alteration of a protein or nucleic acids shape through some form of external stress (for example, by applying heat, acid or alkali), in such a way that it will no... The Siamese is one of the first distinctly recognised breeds of Oriental cat. ...

Siamese cats have a temperature-sensitive mutation in pigment production.

Environment also plays a dramatic role in effects of the human genetic disease phenylketonuria.[47] The mutation that causes phenylketonuria disrupts the ability of the body to break down the amino acid phenylalanine, causing a toxic build-up of an intermediate molecule that, in turn, causes severe symptoms of progressive mental retardation and seizures. If someone with the phenylketonuria mutation is kept on a strict diet that avoids this amino acid, however, they remain normal and healthy. Image File history File linksMetadata Download high-resolution version (1392x1870, 231 KB)[edit] Summary This picture was taken by Chantel Hurlow of a Traditional Siamese Female [edit] Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Download high-resolution version (1392x1870, 231 KB)[edit] Summary This picture was taken by Chantel Hurlow of a Traditional Siamese Female [edit] Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Phenylketonuria (PKU) is an autosomal recessive genetic disorder characterized by a deficiency in the enzyme phenylalanine hydroxylase (PAH). ... Phenyl alanine is an α-amino acid with the formula HO2CCH(NH2)CH2C6H5. ...


Gene regulation

The genome of a given organism contains thousands of genes, but not all these genes need to be active at any given moment. A gene is expressed when it is being transcribed into mRNA (and translated into protein), and there exist many cellular methods of controlling the expression of genes such that proteins are produced only when needed by the cell. Transcription factors are regulatory proteins that bind to the start of genes, either promoting or inhibiting the transcription of the gene.[48] Within the genome of Escherichia coli bacteria, for example, there exists a series of genes necessary for the synthesis of the amino acid tryptophan. However, when tryptophan is already available to the cell, these genes for tryptophan synthesis are no longer needed. The presence of tryptophan directly affects the activity of the genes—tryptophan molecules bind to the tryptophan repressor (a transcription factor), changing the repressor's structure such that the repressor binds to the genes. The tryptophan repressor blocks the transcription and expression of the genes, thereby creating negative feedback regulation of the tryptophan synthesis process.[49] Gene modulation redirects here. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... In molecular biology, a transcription factor is a protein that binds DNA at a specific promoter or enhancer region or site, where it regulates transcription. ... E. coli redirects here. ... Tryptophan (abbreviated as Trp or W)[1] is one of the 20 standard amino acids, which are the building blocks of proteins, and an essential amino acid in the human diet. ... The trp (tryptophan) repressor is a 25 kD protein which regulates transcription of the tryptophan biosynthetic pathway in bacteria. ... This article does not cite any references or sources. ...

Transcription factors bind to DNA, influencing the transcription of associated genes.
Transcription factors bind to DNA, influencing the transcription of associated genes.

Differences in gene expression are especially clear within multicellular organisms, where cells all contain the same genome but have very different structures and behaviors due to the expression of different sets of genes. All the cells in a multicellular organism derive from a single cell, differentiating into different cell types in response to external and intercellular signals and gradually establishing different patterns of gene expression to create different behaviors. No single gene is responsible for the development of structures within multicellular organisms, these patterns arise from the complex interactions between many cells. Image File history File links Download high-resolution version (1188x1114, 410 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Zinc finger Zif268 ... Image File history File links Download high-resolution version (1188x1114, 410 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Zinc finger Zif268 ... Wild-type Caenorhabditis elegans hermaphrodite stained to highlight the nuclei of all cells Multicellular organisms are organisms consisting of more than one cell, and having differentiated cells that perform specialized functions. ... Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. ... Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ...


Within eukaryotes there exist structural features of chromatin that influence the transcription of genes, often in the form of modifications to DNA and chromatin that are stably inherited by daughter cells.[50] These features are called "epigenetic" because they exist "on top" of the DNA sequence and retain inheritance from one cell generation to the next. Because of epigenetic features, different cell types grown within the same medium can retain very different properties. Although epigenetic features are generally dynamic over the course of development, some, like the phenomenon of paramutation, have multigenerational inheritance and exist as rare exceptions to the general rule of DNA as the basis for inheritance.[51] Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Chromatin is the complex of DNA and protein found inside the nuclei of eukaryotic cells. ... Epigenetic inheritance is the transmission of information from a cell or multicellular organism to its descendants without that information being encoded in the nucleotide sequence of the gene. ... Epithelial cells in culture, stained for keratin (red) and DNA (green) Cell culture is the process by which either prokaryotic or eukaryotic cells are grown under controlled conditions. ... Paramutation, in genetics, is an interaction between two alleles of a single locus, resulting in a heritable change of one allele. ...


Genetic change

Gene duplication allows diversification by providing redundancy: one gene can mutate and lose its original function without harming the organism.
Gene duplication allows diversification by providing redundancy: one gene can mutate and lose its original function without harming the organism.

Image File history File links Original source is from the Talking Glossary of Genetics http://www. ... Image File history File links Original source is from the Talking Glossary of Genetics http://www. ...

Mutations

Main article: Mutation

During the process of DNA replication, errors occasionally occur in the polymerization of the second strand. These errors, called mutations, can have an impact on the phenotype of an organism, especially if they occur within the protein coding sequence of a gene. Error rates are usually very low—1 error in every 10–100 million bases—due to the "proofreading" ability of DNA polymerases.[52][53] (Without proofreading error rates are a thousand-fold higher; because many viruses rely on DNA and RNA polymerases that lack proofreading ability they experience higher mutation rates.) Processes that increase the rate of changes in DNA are called mutagenic: mutagenic chemicals promote errors in DNA replication, often by interfering with the structure of base-pairing, while UV radiation induces mutations by causing damage to the DNA structure.[54] Chemical damage to DNA occurs naturally as well, and cells use DNA repair mechanisms to repair mismatches and breaks in DNA—nevertheless, the repair sometimes fails to return the DNA to its original sequence. For linguistic mutation, see Apophony. ... DNA replication. ... This article is about mutation in biology, for other meanings see: mutation (disambiguation). ... In biology, a mutagen (Latin, literally origin of change) is an agent that changes the genetic information (usually DNA) of an organism and thus increases the number of mutations above the natural background level. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... DNA damage resulting in multiple broken chromosomes DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. ...


In organisms that use chromosomal crossover to exchange DNA and recombine genes, errors in alignment during meiosis can also cause mutations.[55] Errors in crossover are especially likely when similar sequences cause partner chromosomes to adopt a mistaken alignment; this makes some regions in genomes more prone to mutating in this way. These errors create large structural changes in DNA sequence—duplications, inversions or deletions of entire regions, or the accidental exchanging of whole parts between different chromosomes (called translocation). Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... For the figure of speech, see meiosis (figure of speech). ... Schematic of a region of a chromosome before and after a duplication event Gene duplication occurs when an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome leads to the duplication of a region of DNA containing a gene [1]. The significance of this process for... An inversion is a chromosome rearrangement in which a segment of a chromosome is reversed end to end. ... A gene deletion, or deletion mutation is a genetic mutation in which a part of a chromosome or a sequence of DNA is missing. ... Chromosomal translocation of the 4th and 20th chromosome. ...


Natural selection and evolution

Main article: Evolution

Mutations produce organisms with different genotypes, and those differences can result in different phenotypes. Many mutations have little effect on an organism's phenotype, health, and reproductive fitness. Mutations that do have an effect are often deleterious, but occasionally mutations are beneficial. This article is about evolution in biology. ... Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. ...

An evolutionary tree of eukaryotic organisms, constructed by comparison of several orthologous gene sequences
An evolutionary tree of eukaryotic organisms, constructed by comparison of several orthologous gene sequences

Population genetics research studies the distributions of these genetic differences within populations and how the distributions change over time.[56] Changes in the frequency of an allele in a population can be influenced by natural selection, where a given allele's higher rate of survival and reproduction causes it to become more frequent in the population over time.[57] Genetic drift can also occur, where chance events lead to random changes in allele frequency.[58] Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... The evolutionary tree of living things is currently supposed to run something along the lines of that listed below. ... Two or more structures are said to be homologous if they are alike because of shared ancestry. ... Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation, and migration. ... For other uses, see Natural selection (disambiguation). ... In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...


Over many generations, the genomes of organisms can change, resulting in the phenomenon of evolution. Mutations and the selection for beneficial mutations can cause a species to evolve into forms that better survive their environment, a process called adaptation.[59] New species are formed through the process of speciation, a process often caused by geographical separations that allow different populations to genetically diverge.[60] This article is about evolution in biology. ... This article is about evolution in biology. ... For other uses, see Adaptation (disambiguation). ... Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...


As sequences diverge and change during the process of evolution, these differences between sequences can be used as a molecular clock to calculate the evolutionary distance between them.[61] Genetic comparisons are generally considered the most accurate method of characterizing the relatedness between species, an improvement over the sometimes deceptive comparison of phenotypic characteristics. The evolutionary distances between species can be combined to form evolutionary trees—these trees represent the common descent and divergence of species over time, although they cannot represent the transfer of genetic material between unrelated species (known as horizontal gene transfer and most common in bacteria). The molecular clock (based on the molecular clock hypothesis (MCH)) is a technique in genetics, which researchers use to date when two species diverged. ... The evolutionary tree of living things is currently supposed to run something along the lines of that listed below. ... A group of organisms is said to have common descent if they have a common ancestor. ... Horizontal gene transfer (HGT), also Lateral gene transfer (LGT), is any process in which an organism transfers genetic material to another cell that is not its offspring. ...


Research and technology

The common fruit fly (Drosophila melanogaster) is a popular model organism in genetics research.
The common fruit fly (Drosophila melanogaster) is a popular model organism in genetics research.

Image File history File links File links The following pages link to this file: Drosophila melanogaster ... Image File history File links File links The following pages link to this file: Drosophila melanogaster ... Binomial name Drosophila melanogaster Meigen, 1830 [1] Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order of the flies. ... A model organism is a species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. ...

Model organisms and genetics

Although geneticists originally studied inheritance in a wide range of organisms, researchers began to specialize in studying the genetics of a particular subset of organisms. The fact that significant research already existed for a given organism would encourage new researchers to choose it for further study, and so eventually a few model organisms became the basis for most genetics research.[62] Common research topics in model organism genetics include the study of gene regulation and the involvement of genes in development and cancer. A model organism is one that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. ... Gene regulation is the general term for cellular control of protein synthesis at the DNA-RNA transcription step. ... Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ...


Organisms were chosen, in part, for convenience—short generation times and facile genetic manipulation made some organisms popular genetics research tools. Widely used model organisms include the gut bacterium Escherichia coli, the plant Arabidopsis thaliana, baker's yeast (Saccharomyces cerevisiae), the nematode Caenorhabditis elegans, the common fruit fly (Drosophila melanogaster), and the common house mouse (Mus musculus). E. coli redirects here. ... Binomial name Arabidopsis thaliana (L.) Heynh. ... Binomial name Meyen ex E.C. Hansen Saccharomyces cerevisiae is a species of budding yeast. ... Binomial name Maupas, 1900 Caenorhabditis elegans (IPA: ) is a free-living nematode (roundworm), about 1 mm in length, which lives in temperate soil environments. ... Binomial name Meigen, 1830[1] Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order of the flies. ... Binomial name Mus musculus Linnaeus, 1758 Mus musculus is the common house mouse. ...


Medical genetics research

Medical genetics seeks to understand how genetic variation relates to human health and disease.[63] When searching for an unknown gene that may be involved in a disease, researchers commonly use genetic linkage and genetic pedigree charts to find the location on the genome associated with the disease. At the population level, researchers take advantage of Mendelian randomization to look for locations in the genome that are associated with diseases, a technique especially useful for multigenic traits not clearly defined by a single gene.[64] Once a candidate gene is found, further research is often done on the same gene (called an orthologous gene) in model organisms. In addition to studying genetic diseases, the increased availability of genotyping techniques has led to the field of pharmacogenetics—studying how genotype can affect drug responses.[65] Medical Genetics is the application of genetics to medicine. ... Genetic linkage occurs when particular alleles are inherited jointly. ... A pedigree chart is a chart which tells one all of the known phenotypes for an organism and its ancestors, most commonly humans, show dogs, and race horses. ... An important focus of observational epidemiology is the identification of modifiable causes of common diseases that are of public health interest. ... Inheritance of quantitative traits refers to the inheritance of a phenotypic characteristic that varies in degree and can be attributed to the interactions between two or more genes and their environment (also called Polygenic inheritance). ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... The terms pharmacogenomics and pharmacogenetics tend to be used interchangeably, and a precise, consensus definition of either remains elusive. ...


Although it is not an inherited disease, cancer is also considered a genetic disease.[66] The process of cancer development in the body is a combination of events. Mutations occasionally occur within cells in the body as they divide—while these mutations will not be inherited by any offspring, they can affect the behavior of cells, sometimes causing them to grow and divide more frequently. There are biological mechanisms that attempt to stop this process—signals are given to inappropriately dividing cells that should trigger cell death, but sometimes additional mutations occur that cause cells to ignore these messages. An internal process of natural selection occurs within the body and eventually mutations accumulate within cells to promote their own growth, creating a cancerous tumor that grows and invades various tissues of the body. Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... For linguistic mutation, see Apophony. ... A section of mouse liver showing an apoptotic cell indicated by an arrow Apoptosis (/̩æ.pÉ™pˈto. ... For other uses, see Natural selection (disambiguation). ...

E coli colonies on a plate of agar, an example of cellular cloning and often used in molecular cloning
E coli colonies on a plate of agar, an example of cellular cloning and often used in molecular cloning

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Binomial name Escherichia coli T. Escherich, 1885 Escherichia coli (usually abbreviated to E. coli) is one of the main species of bacteria that live in the lower intestines of warm-blooded animals (including birds and mammals) and are necessary for the proper digestion of food. ... This is a biological article: For a territory administered by another territory see: Colony For a group attempting to affiliate with a Fraternity or Sorority see: Colony (fraternity) In biology, a colony (from Latin colonia) refers to several individual organisms of the same species living closely together, usually for mutual... This does not adequately cite its references or sources. ... For the cloning of human beings, see human cloning. ... Molecular cloning refers to the procedure of isolating a defined DNA sequence and obtaining multiple copies of it in vivo. ...

Research techniques

DNA can be manipulated in the laboratory. Restriction enzymes are a commonly used enzyme that cuts DNA at specific sequences, producing predictable fragments of DNA.[67] The use of ligation enzymes allows these fragments to be reconnected, and by ligating fragments of DNA together from different sources, researchers can create recombinant DNA. Often associated with genetically modified organisms, recombinant DNA is commonly used in the context of plasmids—short circular DNA fragments with a few genes on them. By inserting plasmids into bacteria and growing those bacteria on plates of agar (to isolate clones of bacteria cells), researchers can clonally amplify the inserted fragment of DNA (a process known as molecular cloning). (Cloning can also refer to the creation of clonal organisms, through various techniques.) A restriction enzyme (or restriction endonuclease) is an enzyme that cuts double-stranded DNA. The enzyme makes two incisions, one through each of the phosphate backbones of the double helix without damaging the bases. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... In molecular biology, DNA ligase is a particular type of ligase (EC 6. ... Recombinant DNA (rDNA) is an artificial DNA sequence resulting from the combination of different DNA sequences. ... GMO redirects here. ... Figure 1 : Schematic drawing of a bacterium with plasmids enclosed. ... For the cloning of human beings, see human cloning. ... For the cloning of human beings, see human cloning. ... For the cloning of human beings, see human cloning. ...


DNA can also be amplified using a procedure called the polymerase chain reaction (PCR).[68] By using specific short sequences of DNA, PCR can isolate and exponentially amplify a targeted region of DNA. Because it can amplify from extremely small amounts of DNA, PCR is also often used to detect the presence of specific DNA sequences. “PCR” redirects here. ...


DNA sequencing and genomics

One of the most fundamental technologies developed to study genetics, DNA sequencing allows researchers to determine the sequence of nucleotides in DNA fragments. Developed in 1977 by Frederick Sanger and coworkers, chain-termination sequencing is now routinely used to sequence DNA fragments.[69] With this technology, researchers have been able to study the molecular sequences associated with many human diseases. As sequencing has become less expensive and with the aid of computational tools, researchers have sequenced the genomes of many organisms by stitching together the sequences of many different fragments (a process called genome assembly).[70] These technologies were used to sequence the human genome, leading to the completion of the Human Genome Project in 2003.[19] The term DNA sequencing encompasses biochemical methods for determining the order of the nucleotide bases, adenine, guanine, cytosine, and thymine, in a DNA oligonucleotide. ... Frederick Sanger, OM, CH, CBE, FRS (born 13 August 1918) is an English biochemist and a two time Nobel laureate in chemistry. ... Genome projects are scientific endeavours that ultimately aim to determine the complete genome sequence of an organism (be it an animal, a plant, a fungus, a bacterium, an archaean, a protist or a virus). ... Genome assembly refers to the process of taking a large number of short DNA sequences, all of which were generated by a shotgun sequencing project, and putting them back together to create a representation of the original chromosomes from which the DNA originated. ... The Human Genome Project (HGP) is an international scientific research project. ...


The large amount of sequences available has created the field of genomics, research that uses computational tools to search for and analyze patterns in the full genomes of organisms. Genomics can also be considered a subfield of bioinformatics, which uses computational approaches to analyze large sets of biological data.
Genomics is the study of an organisms entire genome; Rathore et al, . Investigation of single genes, their functions and roles is something very common in todays medical and biological research, and cannot be said to be genomics but rather the most typical feature of molecular biology. ... Map of the human X chromosome (from the NCBI website). ...


References

  • Alberts B, Johnson A, Lewis J, Raff M, Roberts K, and Walter P (2002). Molecular Biology of the Cell, 4th edition. ISBN 0-8153-3218-1. 
  • Griffiths AJF, Miller JH, Suzuki DT, Lewontin RC, and Gelbart WM (2000). An Introduction to Genetic Analysis. New York: W.H. Freeman and Company. ISBN 0-7167-3520-2. 
  • Hartl D, Jones E (2005). Genetics: Analysis of Genes and Genomes, 6th edition. Jones & Bartlett. ISBN 0-7637-1511-5. 
  • Lodish H, Berk A, Zipursky LS, Matsudaira P, Baltimore D, and Darnell J (2000). Molecular Cell Biology, 4th edition. ISBN 0-7167-3136-3. 

Notes

  1. ^ Griffiths et al. (2000), Chapter 1 (Genetics and the Organism): Introduction
  2. ^ Hartl D, Jones E (2005)
  3. ^ Weiling F (1991). "Historical study: Johann Gregor Mendel 1822–1884". American Journal of Medical Genetics 40 (1): 1–25; discussion 26. PMID 1887835. 
  4. ^ Lamarck, J-B (2008). In Encyclopædia Britannica. Retrieved from Encyclopædia Britannica Online on 2008-03-16.
  5. ^ a b Mendel, GJ (1866). "Versuche über Pflanzen-Hybriden". Verhandlungen des naturforschenden Vereins Brünn 4: 3–47.  (in English in 1901, J. R. Hortic. Soc. 26: 1–32) translation available online
  6. ^ genetics, n., Oxford English Dictionary, 3rd ed.
  7. ^ Bateson W. Letter from William Bateson to Alan Sedgwick in 1905. The John Innes Centre. Retrieved on 2008-03-15.
  8. ^ genetic, adj., Oxford English Dictionary, 3rd ed.
  9. ^ Bateson, W (1907). "The Progress of Genetic Research". Wilks, W (editor) Report of the Third 1906 International Conference on Genetics: Hybridization (the cross-breeding of genera or species), the cross-breeding of varieties, and general plant breeding, London: Royal Horticultural Society. 
    Although the conference was titled "International Conference on Hybridisation and Plant Breeding", Wilks changed the title for publication as a result of Bateson's speech.
  10. ^ Moore JA (1983). "Thomas Hunt Morgan—The Geneticist". American Zoologist 23 (4): 855–865. 
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2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 75th day of the year (76th in leap years) in the Gregorian calendar. ... Written in 1865 by Gregor Mendel, Experiments on Plant Hybridization (German: Versuche über Pflanzen-Hybriden) was the result after years spent studying genetic traits in pea plants. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Horace Freeland Judson is a historian of molecular biology and the author of several books, including The Eighth Day of Creation, a history of molecular biology, and A Great Betrayal: Fraud in Science, an examination of the deliberate manipulation of scientific data. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 77th day of the year (78th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Also see: 2002 (number). ... is the 101st day of the year (102nd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 204th day of the year (205th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 149th day of the year (150th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... The Journal of Biological Chemistry is a scientific journal published by the American Society for Biochemistry and Molecular Biology. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 74th day of the year (75th in leap years) in the Gregorian calendar. ...

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Image File history File links Wikibooks-logo-en. ... Wikibooks logo Wikibooks, previously called Wikimedia Free Textbook Project and Wikimedia-Textbooks, is a wiki for the creation of books. ... Image File history File links Wikiversity-logo-Snorky. ... Wikiversity logo Wikiversity is a Wikimedia Foundation beta project[1], devoted to learning materials and activities, located at www. ... The Open Directory Project (ODP), also known as dmoz (from , its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors. ... Classical genetics consists of the techniques and methodologies of genetics that predate the advent of molecular biology. ... Conservation genetics is a science that aims to apply genetic methods to the maintenance, loss, and restoration of biodiversity. ... Ecological genetics is the study of genetics (itself a field of biology) from an ecological perspective. ... Immunogenetics is the branch of medical research that explores the relationship between the immune system and genetics. ... Molecular genetics is the field of biology which studies the structure and function of genes at a molecular level. ... Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation, and migration. ... Quantitative genetics is the study of continuous traits (such as height or weight) and its underlying mechanisms. ... A geneticist is a scientist who studies genetics, the science of heredity and variation of organisms. ... Genomics is the study of an organisms entire genome; Rathore et al, . Investigation of single genes, their functions and roles is something very common in todays medical and biological research, and cannot be said to be genomics but rather the most typical feature of molecular biology. ... Medical Genetics is the application of genetics to medicine. ... Molecular evolution is the process of the genetic material in populations of organisms changing over time. ... Reverse genetics is an approach to discovering the function of a gene that proceeds in the opposite direction of so called forward genetic screens that are more usual in classical genetics. ... For the song by Girls Aloud see Biology (song) Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: Βιολογία - βίος, bio, life; and λόγος, logos, speech lit. ... Human heart and lungs, from an older edition of Grays Anatomy. ... The DNA structure might not be the only nucleic acid in the universe capable of supporting life[1] Astrobiology (from Greek: ἀστρο, astro, constellation; βίος, bios, life; and λόγος, logos, knowledge) is the interdisciplinary study of life in space, combining aspects of astronomy, biology and geology. ... Wöhler observes the synthesis of urea. ... Map of the human X chromosome (from the NCBI website). ... Biostatistics or biometry is the application of statistics to a wide range of topics in biology. ... Pinguicula grandiflora commonly known as a Butterwort Example of a cross section of a stem [1] Botany is the scientific study of plant life. ... Cell biology (also called cellular biology or formerly cytology, from the Greek kytos, container) is an academic discipline that studies cells. ... Chronobiology is a field of science that examines periodic (cyclic) phenomena in living organisms. ... Views of a Foetus in the Womb, Leonardo da Vinci, ca. ... For the journal, see Ecology (journal). ... Epidemiology is the study of factors affecting the health and illness of populations, and serves as the foundation and logic of interventions made in the interest of public health and preventive medicine. ... This article or section does not cite any references or sources. ... Genomics is the study of an organisms entire genome; Rathore et al, . Investigation of single genes, their functions and roles is something very common in todays medical and biological research, and cannot be said to be genomics but rather the most typical feature of molecular biology. ... Human biology is an interdisciplinary academic field of biology, biological anthropology, and medicine which focuses on humans; it is closely related to primate biology, and a number of other fields. ... Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. ... Various species of reef fish in the Hawaiian Islands. ... An agar plate streaked with microorganisms Microbiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. ... Molecular biology is the study of biology at a molecular level. ... Drawing of the cells in the chicken cerebellum by S. Ramón y Cajal Neuroscience is a field that is devoted to the scientific study of the nervous system. ... The Nutrition Facts table indicates the amounts of nutrients which experts recommend you limit or consume in adequate amounts. ... For the definition, see Life. ... Paleontology, palaeontology or palæontology (from Greek: paleo, ancient; ontos, being; and logos, knowledge) is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ... Adult black fly (Simulium yahense) with (Onchocerca volvulus) emerging from the insects antenna. ... A renal cell carcinoma (chromophobe type) viewed on a hematoxylin & eosin stained slide Pathologist redirects here. ... This article or section does not cite any references or sources. ... Systems biology is a term used very widely in the biosciences, particularly from the year 2000 onwards, and in a variety of contexts. ... Taxonomy, sometimes alpha taxonomy, is the science of finding, describing and naming organisms, thus giving rise to taxa. ... Zoology (from Greek: ζῴον, zoion, animal; and λόγος, logos, knowledge) is the biological discipline which involves the study of animals. ...

  Results from FactBites:
 
Genetics Home Reference - Your guide to understanding genetic conditions (129 words)
The genetics of more than 300 health conditions, diseases, and syndromes.
Genetics Home Reference provides consumer-friendly information about the effects of genetic variations on human health.
Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional.
Genetics - Wikipedia, the free encyclopedia (1779 words)
The word "genetics" was first suggested to describe the study of inheritance and the science of variation by the prominent British scientist William Bateson in a personal letter to Adam Sedgwick, dated April 18, 1905.
The foundational discipline is population genetics which studies the distribution of and change in allele frequencies of genes under the influence of the four evolutionary forces: natural selection, genetic drift, mutation and migration.
While molecular genetics studies the structure and function of genes at a molecular level, ecological genetics focuses on wild populations of organisms, and attempts to collect data on the ecological aspects of individuals as well as molecular markers from those individuals.
  More results at FactBites »

 
 

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