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Encyclopedia > Dominance relationship

In genetics, dominance describes a specific relationship between the effects of different versions of a gene (alleles) on a trait (phenotype). Animals (including humans) and plants are mostly diploid (see ploidy), with two copies of each gene, one inherited from each parent. If the two copies are not identical (not the same allele), their combined effect may be different than the effect of having two identical copies of a single allele. But if the combined effect is the same as the effect of having two copies of one of the alleles, we say that allele's effect is dominant over the other. This article is about the general scientific term. ... For other uses, see Gene (disambiguation). ... An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... Ploidy is the number of homologous sets of chromosomes in a biological cell. ...

For example, having two copies of one allele of the EYCL3 gene causes the eye's iris to be brown, and having two copies of another allele causes the iris to be blue. But having one copy of each allele leads to a brown iris. Thus the brown allele is said to be dominant over the blue allele (and the blue allele is said to be recessive to the brown allele). In anatomy, the iris (plural irises or irides) is the most visible part of the eye of vertebrates, including humans. ...

We now know that in most cases a dominance relationship is seen when the recessive allele is defective. In these cases a single copy of the normal allele produces enough of the gene’s product to give the same effect as two normal copies, and so the normal allele is described as being dominant to the defective allele. This is the case for the eye color alleles described above, where a single functional copy of the ‘brown’ allele causes enough melanin to be made in the iris that the eyes appear brown even when paired with the non-melanin-producing ‘blue’ allele. Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ...

Dominance was discovered by Mendel, who introduced the use of uppercase letters to denote dominant alleles and lowercase to denote recessive alleles, as is still commonly used in introductory genetics courses (e.g. B b for alleles causing brown and blue eyes). Although this usage is convenient it is misleading, because dominance is not a property of an allele considered in isolation but of a relationship between the effects of two alleles. When geneticists loosely refer to a dominant allele or a recessive allele, they mean that the allele is dominant or recessive to the standard allele.

Geneticists often use the term dominance in other contexts, distinguishing between simple or complete dominance as described above, and other relationships. Relationships described as incomplete or partial dominance are usually more accurately described as giving an intermediate or blended phenotype. The relationship described as codominance describes a relationship where the distinct phenotypes caused by each allele are both seen when both alleles are present.

## Nomenclature

A kitten with an mc/mc genotype: the recessive tabby pattern is expressed

Genes are indicated in shorthand by a combination of one or a few letters - for example, in cat coat genetics the alleles Mc and mc (for "mackerel tabby") play a prominent role. Alleles producing dominant traits are denoted by initial capital letters; those that confer recessive traits are written with lowercase letters. The alleles present in a locus are usually separated by a slash, '/'; in the Mc vs mc case, the dominant trait is the "mackerel-stripe" pattern, and the recessive one the "classic" or "oyster" tabby pattern, and thus a classical-pattern tabby cat would carry the alleles mc/mc, whereas a mackerel-stripe tabby would be either Mc/mc or Mc/Mc. Download high resolution version (880x600, 137 KB)red kitten as seen in Agios Georgios, Crete, Greece Author: me, Paul Vlaar Date: 2002-09-05 Source: http://www. ... Download high resolution version (880x600, 137 KB)red kitten as seen in Agios Georgios, Crete, Greece Author: me, Paul Vlaar Date: 2002-09-05 Source: http://www. ... This cats coat allows it to blend in well with its environment The genetics of cat coat coloration, pattern, length, and texture is a complex subject, and many different genes are involved. ... Williamsburg eighteenth century press letters Capital letters or majuscules (in the Roman alphabet: A, B, C, D, ...) are also simply called capitals, caps or upper case; manual typesetters kept them in the upper drawers of a desk, keeping the more frequently used minuscule letters on the lower shelf. ... Minuscule, or lower case, is the smaller form (case) of letters (in the Roman alphabet: a, b, c, ...). Originally alphabets were written entirely in majuscule (capital) letters which were spaced between well-defined upper and lower bounds. ... Short and long arms Chromosome. ...

## Relationship to other genetics concepts

Humans have 23 homologous chromosome pairs (22 pairs of autosomal chromosomes and two distinct sex chromosomes, X and Y). It is estimated that the human genome contains 20,000-25,000 genes[1]. Each chromosomal pair has the same genes, although it is generally unlikely that homologous genes from each parent will be identical in sequence. The specific variations possible for a single gene are called alleles: for a single eye-color gene, there may be a blue eye allele, a brown eye allele, a green eye allele, etc. Consequently, a child may inherit a blue eye allele from their mother and a brown eye allele from their father. The dominance relationships between the alleles control which traits are and are not expressed. Homologous chromosomes are chromosomes in a biological cell that pair (synapse) during meiosis, or alternatively, non-identical chromosomes that contain information for the same biological features and contain the same genes at the same loci but possibly different genetic information, called alleles, at those genes. ... An autosome is a non-sex chromosome. ... A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ...

An example of an autosomal dominant human disorder is Huntington's disease, which is a neurological disorder resulting in impaired motor function. The mutant allele results in an abnormal protein, containing large repeats of the amino acid glutamine. This defective protein is toxic to neural tissue, resulting in the characteristic symptoms of the disease. Hence, one copy suffices to confer the disorder. A representation of the 3D structure of myoglobin showing coloured alpha helices. ... This article is about the class of chemicals. ... Glutamine (abbreviated as Gln or Q; Glx or Z represents either glutamine or glutamic acid) is one of the 20 amino acids encoded by the standard genetic code. ...

A list of human traits that follow a simple inheritance pattern can be found in human genetics. Humans have several genetic diseases, often but not always caused by recessive alleles. A karyotype of a human male, showing 46 chromosomes including XY sex chromosomes. ... A genetic disorder, or genetic disease is a disease caused, at least in part, by the genes of the person with the disease. ...

## Punnett square

Main article: Punnett square

The genetic combinations possible with simple dominance can be expressed by a diagram called a Punnett square. One parent's alleles are listed across the top and the other parent's alleles are listed down the left side. The interior squares represent possible offspring, in the ratio of their statistical probability. In the previous example of flower color, P represents the dominant purple-colored allele and p the recessive white-colored allele. If both parents are purple-colored and heterozygous (Pp), the Punnett square for their offspring would be: 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. ... 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. ... Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. ...

 P p P P P P p p P p p p

In the PP and Pp cases, the offspring is purple colored due to the dominant P. Only in the pp case is there expression of the recessive white-colored phenotype. Therefore, the phenotypic ratio in this case is 3:1, meaning that F2 generation offspring will be purple-colored three times out of four, on average.

• Note: Dominant alleles are capitalized.

## Dominant allele

Dominant trait refers to a genetic feature that hides the recessive trait in the phenotype of an individual. A dominant trait is a phenotype that is seen in both the homozygous AA and heterozygous Aa genotypes. Many traits are determined by pairs of complementary genes, each inherited from a single parent. Often when these are paired and compared, one allele (the dominant) will be found to effectively shut out the instructions from the other, recessive allele. For example, if a person has one allele for blood type A and one for blood type O, that person will always have blood type A. For a person to have blood type O, both their alleles must be O (recessive).

When an individual has two dominant alleles (AA), the condition is referred to as homozygous dominant; an individual with two recessive alleles (aa) is called homozygous recessive. An individual carrying one dominant and one recessive allele is referred to as heterozygous.

A dominant trait when written in a genotype is always written before the recessive gene in a heterozygous pair. A heterozygous genotype is written Aa, not aA.

### Types of dominances

#### Simple dominance or complete dominance

Consider the simple example of flower color in peas, first studied by Gregor Mendel. The dominant allele is purple and the recessive allele is white.[verification needed] In a given individual, the two corresponding alleles of the chromosome pair fall into one of three patterns: â€œMendelâ€ redirects here. ...

• both alleles purple (PP)
• both alleles white (pp)
• one allele purple and one allele white (Pp)

If the two alleles are the same (homozygous), the trait they represent will be expressed. But if the individual carries one of each allele (heterozygous), only the dominant one will be expressed. The recessive allele will simply be suppressed. 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. ...

##### Simple dominance in pedigrees

Dominant traits are recognizable by the fact that they do not skip generations, as recessive traits do. It is therefore quite possible for two parents with purple flowers to have white flowers among their progeny, but two such white offspring could not have purple offspring (although very rarely, one might be produced by mutation). In this situation, the purple individuals in the first generation must have both been heterozygous (carrying one copy of each allele). For linguistic mutation, see Apophony. ...

#### Incomplete dominance

Discovered by Karl Correns, incomplete dominance (sometimes called partial dominance) is a heterozygous genotype that creates an intermediate phenotype. In this case, only one allele (usually the wild type) at the single locus is expressed in a doseage dependent manner, which results in an intermediate phenotype. A cross of two intermediate phenotypes (= monohybrid heterozygotes) will result in the reappearance of both parent phenotypes and the intermediate phenotype. There is a 1:2:1 phenotype ratio instead of the 3:1 phenotype ratio found when one allele is dominant and the other is recessive. This lets an organism's genotype be diagnosed from its phenotype without time-consuming breeding tests. Short and long arms Chromosome. ...

The classic example of this is the color of carnations. Binomial name L. The carnation (Dianthus caryophyllus) is a flowering plant native to the Near East and has been cultivated for the last 2,000 years. ...

 R R' R RR RR' R' RR' R'R'

R is the allele for red pigment. R' is the allele for no pigment.

Thus, RR offspring make a lot of red pigment and appear red. R'R' offspring make no red pigment and appear white. Both RR' and R'R offspring make some pigment and therefore appear pink.

A readily visible example of incomplete dominance is the color modifier Merle in dogs. Blue merle Border Collie puppy Merle is a colour combination in dogsâ€™ coats. ...

#### Codominance

In codominance, neither phenotype is recessive. Instead, the heterozygous individual expresses both phenotypes. A common example is the ABO blood group system. The gene for blood types has three alleles: A, B, and i. i causes O type and is recessive to both A and B. The A and B alleles are codominant with each other. When a person has both an A and a B allele, the person has type AB blood. ABO blood group antigens present on red blood cells and IgM antibodies present in the serum The ABO blood group system is the most important blood type system (or blood group system) in human blood transfusion. ...

When two persons with AB blood type have children, the children can be type A, type B, or type AB. There is a 1A:2AB:1B phenotype ratio instead of the 3:1 phenotype ratio found when one allele is dominant and the other is recessive. This is the same phenotype ratio found in matings of two organisms that are heterozygous for incomplete dominant alleles.

Example Punnett square for a father with A and i, and a mother with B and i:

 A i B AB B i A O

Amongst the very few codominant genetic diseases in humans, one relatively common one is A1AD, in which the genotypes Pi00, PiZ0, PiZZ, and PiSZ all have their more-or-less characteristic clinical representations. Alpha 1-antitrypsin deficiency (A1AD or Alpha-1) is a genetic disorder caused by reduced levels of alpha 1_antitrypsin in the blood. ... This article does not cite any references or sources. ...

Most molecular markers are considered to be codominant.

A roan horse has codominant follicle genes, expressing individual red and white follicles. A red roan horse Roan is a type of coat color in horses (and, occasionally, in other animals, such as dogs and cattle) that is a mixture of white hairs with a base coat of another color. ...

#### Dominant negative

Some loss-of-function mutations are dominant and are called "dominant negative" or antimorphic mutations. Typically, a dominant negative mutation occurs when the gene product adversely affects the normal, wild-type gene product within the same cell. This usually occurs if the product can still interact with the same elements as the wild-type product, but block some aspect of its function. Such proteins may be competitive inhibitors of the normal protein functions. 1946 Nobel Prize winner Hermann J. Muller (1890-1967) coined the terms amorph, hypomorph, hypermorph, antimorph and neomorph to classify mutations based on their behaviour in various genetic situations. ... In biochemistry there are three ways in which certain chemical substances may reduce or prevent the activities of enzymes: competitive, non-competitive and uncompetitive inhibition. ...

Types:

• A mutation in a transcription factor that removes the activation domain, but still contains the DNA binding domain. This product can then block the wild-type transcription factor from binding the DNA site leading to reduced levels of gene activation.
• A protein that is functional as a dimer. A mutation that removes the functional domain, but retains the dimerization domain would cause a dominant negative phenotype, because some fraction of protein dimers would be missing one of the functional domains.

### Autosomal dominant gene

Autosomal Dominant Pedigree Chart

An autosomal dominant gene is one that occurs on an autosomal (non-sex determining) chromosome. As it is dominant, the phenotype it gives will be expressed even if the gene is heterozygous. This contrasts with recessive genes, which need to be homozygous to be expressed. Image File history File links Autosomal_Dominant_Pedigree_Chart. ... Image File history File links Autosomal_Dominant_Pedigree_Chart. ... For other uses, see Gene (disambiguation). ... An autosome is a non-sex chromosome. ... A scheme of a condensed (metaphase) chromosome. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. ... 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). ... Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ...

The chances of an autosomal dominant disorder being inherited are 50% if one parent is heterozygous for the mutant gene and the other is homozygous for the normal, or 'wild-type', gene. This is because the offspring will always inherit a normal gene from the parent carrying the wild-type genes, and will have a 50% chance of inheriting the mutant gene from the other parent. If the mutant gene is inherited, the offspring will be heterozygous for the mutant gene, and will suffer from the disorder. If the parent with the disorder is homozygous for the gene, the offspring produced from mating with an unaffected parent will always have the disorder. See Mendelian inheritance. 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. ...

The term vertical transmission refers to the concept that autosomal dominant disorders are inherited through generations. This is obvious when you examine the pedigree chart of a family for a particular trait. Because males and females are equally affected, they are equally likely to have affected children. Vertical transmission refers to transmission of an infection, such as HIV, hepatitis B, or hepatitis C, from mother to child during the perinatal period, the period immediately before and after birth. ... 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. ...

Although the mutated gene should be present in successive generations in which there are more than one or two offspring, it may appear that a generation is skipped if there is reduced penetrance. Penetrance is a term used in genetics that describes the extent to which the properties controlled by a gene, its phenotype, will be expressed. ...

## Recessive allele

The term "recessive allele" refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in homozygous genotypes (organisms that have two copies of the same allele) and never in heterozygous genotypes. Every diploid organism, including humans, has two copies of every gene on autosomal chromosomes, one from the mother and one from the father. The dominant allele of a gene will always be expressed while the recessive allele of a gene will be expressed only if the organism has two recessive forms.[2] Thus, if both parents are carriers of a recessive trait, there is a 25% chance with each child to show the recessive trait. 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. ... An autosome is a non-sex chromosome. ...

The term "recessive allele" is part of the laws of Mendelian inheritance formulated by Gregor Mendel. Examples of recessive traits in Mendel's famous pea plant experiments include the color and shape of seed pods and plant height.

### Autosomal recessive allele

Relationship between two carrier parents and probabilities of children being unaffected, carriers, or affected

Autosomal recessive is a mode of inheritance of genetic traits located on the autosomes (the pairs of non-sex determining chromosomes - in humans 22). Wikipedia does not yet have an article with this exact name. ... Wikipedia does not yet have an article with this exact name. ... This article or section does not adequately cite its references or sources. ... An autosome is a non-sex chromosome. ... A scheme of a condensed (metaphase) chromosome. ...

In opposition to autosomal dominant trait, a recessive trait only becomes phenotypically apparent when two similar alleles of a gene are present. In other words, the subject is homozygous for the trait. It has been suggested that this article or section be merged into Dominance relationship. ... Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ...

The frequency of the carrier state can be calculated by the Hardy-Weinberg formula: p2 + 2pq + q2 = 1 (p is the frequency of one pair of alleles, and q = 1 − p is the frequency of the other pair of alleles.) Hardyâ€“Weinberg principle for two alleles: the horizontal axis shows the two allele frequencies p and q, the vertical axis shows the genotype frequencies and the three possible genotypes are represented by the different glyphs In population genetics, the Hardyâ€“Weinberg principle is a relationship between the frequencies of alleles...

Recessive genetic disorders occur when both parents are carriers and each contributes an allele to the embryo, meaning these are not dominant genes. As both parents are heterozygous for the disorder, the chance of two disease alleles landing in one of their offspring is 25% (in autosomal dominant traits this is higher). 50% of the children (or 2/3 of the remaining ones) are carriers. When one of the parents is homozygous, the trait will only show in his/her offspring if the other parent is also a carrier. In that case, the chance of disease in the offspring is 50%. A genetic disorder is a condition caused by abnormalities in genes or chromosomes. ... An allele (pronounced , ) (from the Greek Î±Î»Î»Î·Î»Î¿Ï‚, meaning each other) is one member of a pair or series of different forms of a gene. ... For other uses, see Embryo (disambiguation). ... Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. ... It has been suggested that this article or section be merged into Dominance relationship. ... Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ...

### Nomenclature of recessiveness

Technically, the term "recessive gene" is imprecise because it is not the gene that is recessive but the phenotype (or trait). It should also be noted that the concepts of recessiveness and dominance were developed before a molecular understanding of DNA and before molecular biology, thus mapping many newer concepts to "dominant" or "recessive" phenotypes is problematic. Many traits previously thought to be recessive have mild forms or biochemical abnormalities that arise from the presence of the one copy of the allele. This suggests that the dominant phenotype is dependent upon having two dominant alleles, and the presence of one dominant and one recessive allele creates some blending of both dominant and recessive traits. For other uses, see Gene (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. ... Molecular biology is the study of biology at a molecular level. ...

### Examples

#### Pea Plant

Gregor Mendel performed many experiments on pea plant (Pisum sativum) while researching traits, chosen because of the simple and low variety of characteristics, as well as the short period of germination. He experimented with color (green vs. yellow), size (short vs. tall), pea texture (smooth vs. wrinkled), and many others. By good fortune, the characteristics displayed by these plants clearly exhibited a dominant and recessive form. This is not true for many organisms. â€œMendelâ€ redirects here. ... Binomial name Pisum sativum A pea (Pisum sativum) is the small, edible round green seed which grows in a pod on a leguminous vine, hence why it is called a legume. ...

For example, when testing the color of the pea plants, he chose two yellow plants, since yellow was more common than green. He mated them, and examined the offspring. He continued to mate only those that appeared yellow, and eventually, the green ones would stop being produced. He also mated the green ones together and determined that only green ones were produced.

Mendel determined that this was because green was a recessive trait which only appeared when yellow, the dominant trait, was not present. Also, he determined that the dominant trait would be displayed whether or not the recessive trait was there.

#### Autosomal recessive disorders

Dominance/recessiveness refers to phenotype, not genotype. An example to prove the point is sickle cell anemia. The sickle cell genotype is caused by a single base pair change in the beta-globin gene: normal=GAG (glu), sickle=GTG (val). Sickle-shaped red blood cells Sickle cell anemia (American English), sickle cell anaemia (British English) or sickle cell disease is a genetic disease in which red blood cells may change shape under certain circumstances. ... Glutamic acid (Glu, E), is the protonated form of glutamate (the anion). ... Valine is an amino acid that cannot be synthesized by humans, so it is considered an essential amino acid for human life. ...

There are several phenotypes associated with the sickle genotype:

1. anemia (a recessive trait)
2. blood cell sickling (co-dominant)
3. altered beta-globin electrophoretic mobility (co-dominant)
4. resistance to malaria (dominant)

This example demonstrates that one can only refer to dominance/recessiveness with respect to individual phenotypes. This article discusses the medical condition. ... Malaria is a vector-borne infectious disease caused by protozoan parasites. ...

Other recessive disorders:

Albino redirects here. ... Alpha 1-antitrypsin deficiency (A1AD or Alpha-1) is a genetic disorder caused by defective production of alpha 1-antitrypsin, deficient activity in the blood and lungs, and deposition of excessive amounts of abnormal A1AT protein in liver cells. ... Bloom syndrome is a rare inherited disorder characterized by a high frequency of breaks and rearrangements in an affected persons chromosomes, discovered and first described by dermatologist Dr. David Bloom in 1954. ... Spinal Muscular Atrophy (SMA) is a term applied to a number of different disorders, all having in common a genetic cause and the manifestation of weakness due to loss of the motor neurons of the spinal cord and brainstem. ... Chronic granulomatous disease (CGD) is a diverse group of hereditary diseases in which certain cells of the immune system have difficulty forming the reactive oxygen compounds (most importantly, the superoxide radical) used to kill certain ingested pathogens. ... Congenital adrenal hyperplasia (CAH) refers to any of several autosomal recessive diseases resulting from defects in steps of the synthesis of cortisol from cholesterol by the adrenal glands. ... Wet-type human earwax on a cotton swab. ... Dubin-Johnson syndrome is an autosomal recessive disease which presents shortly after birth with an increase of conjugated bilirubin without elevation of liver enzymes (ALT, AST). ... Familial Mediterranean fever (FMF) is a hereditary inflammatory disorder that affects groups of patients originating from around the Mediterranean Sea (hence its name). ... Fanconi anemia (FA) is a genetic disease that affects children and adults from all ethnic backgrounds. ... Friedreichs ataxia is a rare autosomal recessive disorder caused by a mutation in Gene X25 that codes for frataxin, located on chromosome 9. ... Galactosemia is a rare genetic metabolic disorder which affects an individuals ability to properly digest the sugar galactose. ... Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive hereditary disease featuring nonimmune hemolytic anemia in response to a number of causes. ... Glycogen storage disease is any one of several inborn errors of metabolism that result from enzyme defects that affect the processing of glycogen synthesis or breakdown within muscles, liver, and other cell types. ... Haemochromatosis, also spelled hemochromatosis, is a hereditary disease characterized by improper dietary iron metabolism (making it an iron overload disorder), which causes the accumulation of iron in a number of body tissues. ... Homocystinuria, also known as Cystathionine beta synthase deficiency, is inherited disorder of the metabolism of the amino acid methionine. ... The mucopolysaccharidoses are a group of inherited metabolic diseases caused by the absence or malfunctioning of lysosomal enzymes needed to break down molecules called glycosaminoglycans - long chains of sugar carbohydrates in each of our cells that help build bone, cartilage, tendons, corneas, skin and connective tissue. ... Pendred syndrome or Pendred disease is a genetic disorder leading to sensorineural hearing loss and goitre with occasional hypothyroidism. ... Phenylketonuria (PKU) is an autosomal recessive genetic disorder characterized by a deficiency in the enzyme phenylalanine hydroxylase (PAH). ... Polycystic kidney disease (PKD) is a progressive, genetic disorder of the kidneys. ... Rotor syndrome is a rare, benign autosomal recessive disorder of unknown origin. ... Tay-Sachs disease (abbreviated TSD, also known as GM2 gangliosidosis, Hexosaminidase A deficiency or Sphingolipidosis) is a genetic disorder, fatal in its most common variant known as Infantile Tay-Sachs disease. ... Thalassemia (British spelling, thalassaemia) is an inherited autosomal recessive blood disease. ... Wilsons disease or hepatolenticular degeneration is an autosomal recessive hereditary disease, with an incidence of about 1 in 30,000 in most parts of the world and a male preponderance. ... Xeroderma pigmentosum, or XP, is an autosomal recessive genetic disorder of DNA repair in which the bodys normal ability to remove damage caused by ultraviolet (UV) light is deficient. ...

## Mechanisms of dominance

Many genes code for enzymes. Consider the case where someone is homozygous for some trait. Both alleles code for the same enzyme, which causes a trait. Only a small amount of that enzyme may be necessary for a given phenotype. The individual therefore has a surplus of the necessary enzyme. Let's call this case "normal". Individuals without any functional copies cannot produce the enzyme at all, and their phenotype reflects that. Consider a heterozygous individual. Since only a small amount of the normal enzyme is needed, there is still enough enzyme to show the phenotype. This is why some alleles are dominant over others. Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ...

In the case of incomplete dominance, the single dominant allele does not produce enough enzyme, so the heterozygotes show some different phenotype. For example, fruit color in eggplants is inherited in this manner. A purple color is caused by two functional copies of the enzyme, with a white color resulting from two non-functional copies. With only one functional copy, there is not enough purple pigment, and the color of the fruit is a lighter shade, called violet. Aubergine redirects here. ...

Some non-normal alleles can be dominant. The mechanisms for this are varied, but one simple example is when the functional enzyme E is composed of several subunits $E= E_1cdots E_n$ where each Ei is made of several alleles Ei = ai1ai2, with $a_{i1},a_{i2}inlbrace A_i,A_i'rbrace$ making them either functional or not functional according to one of the schemes described above. For example one could have the rule that if any of the Ei subunits are nonfunctional, the entire enzyme E is nonfunctional in the sense that the phenotype is not displayed. In the case of a single subunit say E1 is E1 = F where F has a functional and nonfunctional allele (heterozygous individual)(F = a1A1) , the concentration of functional enzyme determined by E could be 50% of normal. If the enzyme has two identical subunits ($E = FFcdots E_n$ the concentration of functional enzyme is 25% of normal. For four subunits, $E=FFFFcdots E_n$ the concentration of functional enzyme is about 6% of normal (roughly scaling slower than 1 / 2c where c is the number of copies of the allele ( 1 / 24 is about 51% percent) This may not be enough to produce the wild type phenotype. There are other mechanisms for dominant mutants.

## Other factors

It is important to note that most genetic traits are not simply controlled by a single set of alleles. Often many alleles, each with their own dominance relationships, contribute in varying ways to complex traits.

Some medical conditions may have multiple inheritance patterns, such as in centronuclear myopathy or myotubular myopathy, where the autosomal dominant form is on chromosome 19 but the sex-linked form is on the X chromosome. Note: Centronuclear myopathy includes Myotubular myopathy, as outlined below. ... Note: Centronuclear myopathy includes Myotubular myopathy, as outlined below. ... Chromosome 19 is one of the 23 pairs of chromosomes in humans. ... Sex-linked genes are those carried on the mammalian X chromosome but not the Y chromosome. ... â€¹ The template below (Expand) is being considered for deletion. ...

Mitochondrial DNA (some captions in German) Mitochondrial DNA (mtDNA) is the DNA located in organelles called mitochondria. ... It has been suggested that sex chromosome be merged into this article or section. ... Several inheritable traits or congenital conditions in humans are classical examples of Mendelian inheritance: Their presence is controlled by a single gene that can either be of the autosomal-dominant or -recessive type. ...

## Notes

1. ^ How Many Genes Are There? (October 27, 2004).
2. ^ ipse, PennStateUniv.. DNA Determines Your Appearance.
Morphogenesis (from the Greek morphÃª shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... The genotype-phenotype distinction refers to the fact that while genotype and phenotype of an organism are related, they do not necessarily coincide. ... In ecology and genetics, a norm of reaction describes the pattern of phenotypic expression of a single genotype across a range of environments. ... Gene-environment interaction is a term used to describe any phenotypic effects that are due to interactions between the environment and genes. ... In genetics, heritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. ... Quantitative genetics is the study of continuous traits (such as height or weight) and its underlying mechanisms. ... Genetic architecture refers to the underlying genetic basis of a phenotypic trait. ... Epistasis takes place when the action of one gene is modified by one or more others that assort somewhat independently. ... 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). ... Pleiotropy occurs when a single gene influences multiple phenotypic traits. ... We dont have an article called Phenotypic plasticity Start this article Search for Phenotypic plasticity in. ... Norms of reaction for two genotypes. ... In evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes (or phenotypes) and replicatory success. ... Epigenetics is a term in biology used today to refer to features such as chromatin and DNA modifications that are stable over rounds of cell division but do not involve changes in the underlying DNA sequence of the organism. ... A maternal effect, in genetics, is the phenomena where the genotype of a mother is expressed in the phenotype of its offspring. ... Dual inheritance theory, (or DIT), in sharp contrast to the notion that culture overrides biology, posits that humans are products of the interaction between biological evolution and cultural evolution. ... Vertebrates have a segmented vertebral column and brain. ... Many organisms consist of modules, both anatomically and in their metabolism. ... Evolvability is a concept in that relates ability of a particular phenotype to be robust to mutations. ... Mutational robustness describes the extent to which an organisms phenotype remains constant in spite of mutation. ... The evolution of sex is a major puzzle in modern evolutionary biology. ... Conrad Hal Waddington (1905 â€” 1975), known to his friends as Wad, was a developmental biologist, paleontologist, geneticist, embryologist and philosopher. ... Richard Lewontin Richard Charles Dick Lewontin (born March 29, 1929) is an American evolutionary biologist, geneticist and social commentator. ... The nature versus nurture debates concern the relative importance of an individuals innate qualities (nature) versus personal experiences (nurture) in determining or causing individual differences in physical and behavioral traits. ... This is a list of topics in evolutionary biology and evolution. ...

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 Dominance relationship - Wikipedia, the free encyclopedia (1112 words) The dominant/recessive relationship is made possible by the fact that most higher organisms are diploid: that is, most of their cells have two copies of each chromosome -- one copy from each parent. The specific variations possible for a single gene are called alleles: for a single eye-colour gene, there may be a blue eye allele, a brown eye allele, a green eye allele, etc. Consequently, a child may inherit a blue eye allele from their mother and a brown eye allele from their father. An example of incomplete dominance in humans is mordan, a trait that is exhibited when eye color alleles from the maternal and paternal chromosomes are blended.
 Dominance - Wikipedia, the free encyclopedia (172 words) Dominance (biology) in biology and anthropology is the state of having high social status relative to other individuals, who react submissively to dominant individuals. Domination and submission (BDSM) or domination is a term used for a form of human sexuality also referred to in the acronym BDSM. Dominance relationship in genetics refers a property of genes that help to determine whether an offspring will inherit a characteristic from the father, the mother, or some blend of both.
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