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Encyclopedia > Epigenetics
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This article is part of the series on: Image File history File links Broom_icon. ...


Gene expression
a Molecular biology topic (portal)
(Glossary) 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... Molecular biology is the study of biology at a molecular level. ... See also: gene expression, List of Glossaries, List of Natural Sciences Glossaries A constitutive gene or constitutive expression describes a gene that is transcribed continually compared to a facultative gene which is only transcribed when needed. ...

Introduction to Genetics
General flow: DNA > RNA > Protein
special transfers (RNA > RNA,
RNA > DNA, Protein > Protein)
Genetic code
Transcription
Transcription (Transcription factors,
RNA Polymerase,promoter)
post-transcriptional modification
(hnRNA,Splicing)
Translation
Translation (Ribosome,tRNA)
post-translational modification
(functional groups, peptides,
structural changes
)
gene regulation
epigenetic regulation (Hox genes,
Genomic imprinting)
transcriptional regulation
post-transcriptional regulation
(sequestration,
alternative splicing,miRNA)
post-translational regulation
(reversible,irrevesible)

In biology, the term epigenetics refers to changes in gene expression that are stable between cell divisions, and sometimes between generations, but do not involve changes in the underlying DNA sequence of the organism.[1] The idea is that environmental factors can cause an organism's genes to behave (or "express themselves") differently, even though the genes themselves don't change.[2] Epigenetic changes in eukaryotic biology are most elegantly illustrated by the process of cellular differentiation where pluripotent stem cells become the various cell lines of the embryo. This process becomes stable by mechanisms which may include silencing of some genes, removal of silencing marks on some other genes and permanently inactivating still other genes.[3] Animation of a section of DNA rotating. ... 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 interaction of mRNA in a eukaryote cell. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... 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... RNA dependent RNA polymerase, or RDRP, is an enzyme that catalyzes the replication of RNA from an RNA template. ... Reverse transcriptase is an enzyme used by all retroviruses and retrotransposons that transcribes the genetic information from the virus or retrotransposon from RNA into DNA, which can integrate into the host genome. ... For the bird, see Prion (bird). ... For a non-technical introduction to the topic, see Introduction to Genetics. ... A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... In the context of genetics, a transcription factor is a regulatory protein that initiates the transcription of certain genes upon binding with DNA. The binding of a transcription factor to a specific DNA sequence can result in either an increased rate of transcription of the gene, known as activated transcription... This article does not cite any references or sources. ... A promoter is a regulatory region of DNA located upstream (towards the 5 region) of a gene, providing a control point for regulated gene transcription. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... ... In genetics, splicing is a modification of genetic information prior to translation. ... Translation is the second stage of protein biosynthesis (part of the overall process of gene expression). ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ... Posttranslational modification means the chemical modification of a protein after its translation. ... Gene regulation is the general term for cellular control of protein synthesis at the DNA-RNA transcription step. ... A homeobox is a stretch of DNA sequence found in genes involved in the regulation of the development (morphogenesis) of animals, fungi and plants. ... Genomic imprinting is a genetic phenomenon involved in the control of a small proportion of genes in the genome, where the allele that is expressed is determined solely on which parent contributes it. ... Transcriptional regulation is the mechanism that coordinates the expression of DNA with the needs of various life processes such as development, gestation and metabolism. ... Also called GW or Dcp bodies, processing bodies are microscopic structures within the eukaryotic cell made up of many proteins and inactive mRNAs. ... Various modes of alternative splicing Alternative splicing is the process that occurs in eukaryotes in which the splicing process of a pre-mRNA transcribed from one gene can lead to different mature mRNA molecules and therefore to different proteins. ... In genetics, a miRNA (micro-RNA) is a form of single-stranded RNA which is typically 20-25 nucleotides long, and is thought to regulate the expression of other genes. ... A phosphorylated serine residue Phosphorylation is the addition of a phosphate (PO4) group to a protein molecule or a small molecule. ... Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion. ... In biology, epigenesis has at least two distinct meanings: the unfolding development of an organism, and in particular the development of a plant or animal from an egg or spore through a sequence of steps in which cells differentiate and organs form; the theory that plants and animals develop in... For other uses, see Biology (disambiguation). ... For other uses, see Gene (disambiguation). ... 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... Mitosis divides genetic information during cell division. ... 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. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... 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. ... In cell biology, a pluripotent cell is one able to differentiate into many cell types. ... Mouse embryonic stem cells. ... Epithelial cells in culture, stained for keratin (red) and DNA (green) Cell culture is the term applied when growing cells in a synthetic environment. ... For other uses, see Embryo (disambiguation). ... Gene silencing is a general term describing epigenetic processes of gene regulation. ... For other uses, see Gene (disambiguation). ...

Contents

The Molecular basis of epigenetics

The molecular basis of epigenetics involves modifications to DNA and the chromatin proteins that associate with it. Epigenetic states are inherited when cells divide, and although most of these states are considered dynamic over the course of development in multicellular organisms, some epigenetic features show transgenerational inheritance and are inherited from one generation to the next.[4] Specific epigenetic processes include paramutation, bookmarking, imprinting, gene silencing, X chromosome inactivation, position effect, reprogramming, transvection, maternal effects, the progress of carcinogenesis, many effects of teratogens, regulation of histone modifications and heterochromatin, and technical limitations affecting parthenogenesis and cloning. 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. ... Chromatin is the complex of DNA and protein found inside the nuclei of eukaryotic cells. ... Paramutation, in genetics, is an interaction between two alleles of a single locus, resulting in a heritable change of one allele. ... Bookmarking is a biological phenomenon believed to function as an epigenetic mechanism for transmitting cellular memory of the pattern of gene expression in a cell through mitosis to its daughter cells. ... Genomic imprinting is the phenomenon whereby a small subset of all the genes in the genome are expressed according to their parent of origin. ... Gene silencing is a general term describing epigenetic processes of gene regulation. ... In those species in which sex is determined by the presence of the Y or W chromosome rather than the diploidy of the X or Z, a Barr body is the inactive X chromosome in a female cell, or the inactive Z in a male. ... Position effect is the effect on the expression of a gene when its location in a chromosome is changed, often by translocation. ... Reprogramming refers to erasure and reestablishment of DNA methylation during mammalian development. ... Transvection, in genetics, is a process in which the gene regulatory sequence of one allele on a chromosome interact with the coding sequence of the allele on the homologous chromosome. ... A maternal effect, in genetics, is the phenomena where the genotype of a mother is expressed in the phenotype of its offspring. ... Cancers are caused by a series of mutations. ... Teratogenesis is a medical term from the Greek, literally meaning monster making. ... Schematic representation of the assembly of the core histones into the nucleosome. ... For differently-colored eyes, see Heterochromia. ... For the religious belief, see Virgin Birth of Jesus. ... For the cloning of human beings, see human cloning. ...


Epigenetic research uses a wide range of molecular biologic techniques to further our understanding of epigenetic phenomena, including chromatin immunoprecipitation (together with its large-scale variants ChIP-on-chip and ChIP-seq), fluorescent in situ hybridization, methylation-sensitive restriction enzymes, DNA adenine methyltransferase identification (DamID) and bisulfite sequencing. Furthermore, the use of bioinformatic methods is playing an increasing role (computational epigenetics). Chromatin immunoprecipitation (ChIP) assay, is an experimental method used in molecular biology. ... Workflow overview of a ChIP-on-chip experiment. ... A metaphase cell positive for the bcr/abl rearrangement using FISH. The chromosomes can be seen in blue. ... 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. ... Figure 1: Outline of bisulfite conversion of sample sequence of genomic DNA. Nucleotides in blue are unmethylated cytosines converted to uracils by bisulfite, while red nucleotides are 5-methylcytosines resistant to conversion. ... Bioinformatics or computational biology is the use of techniques from applied mathematics, informatics, statistics, and computer science to solve biological problems. ...


Etymology and definitions

The word "epigenetics" has been associated with many different definitions, and much of the confusion surrounding the use of the word "epigenetics" relates to the fact that it was originally defined to explain phenomena without knowing their molecular basis and with time became narrowly linked to certain phenomena as their molecular basis was discovered.[5]


The word "epigenetics" (as in "epigenetic landscape") was coined by C. H. Waddington in 1942 as a portmanteau of the words "genetics" and "epigenesis".[6] Epigenesis is an older word used to describe the differentiation of cells from a totipotent state in embryonic development (used in contrast to "preformationism"). At the time Waddington first used the term "epigenetics," the physical nature of genes and their role in heredity was not known. Epigenetics was Waddington's model of how genes within a multicellular organism interact with their surroundings to produce a phenotype. Because all cells within an organism inherit the same DNA sequences, cellular differentiation processes crucial for epigenesis rely strongly on epigenetic rather than genetic inheritance. Robin Holliday defined epigenetics as "the study of the mechanisms of temporal and spatial control of gene activity during the development of complex organisms."[7] Thus, the word "epigenetic" can be used to describe any aspect other than DNA sequence that influences the development of an organism. Epigenetic landscape is a metaphor for biological development. ... Conrad Hal Waddington FRS FRSE (1905 — 1975) was a developmental biologist, paleontologist, geneticist, embryologist and philosopher who laid the foundations for systems biology. ... A portmanteau (IPA: ) is a word or morpheme that fuses two or more words or word parts to give a combined or loaded meaning. ... This article is about the general scientific term. ... In biology, epigenesis has at least two distinct meanings: the unfolding development of an organism, and in particular the development of a plant or animal from an egg or spore through a sequence of steps in which cells differentiate and organs form; the theory that plants and animals develop in... Totipotency is the ability of a single cell, usually a stem cell, to divide and produce all the differentiated cells in an organism, including extraembrionic tissues. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... In the center of the diagram are three of the early steps in the development of a mammal. ... Robin Holliday proposed a mechanism of DNA-strand exchange that attempted to explain gene-conversion events that occur during meiosis in fungi. ...


Another usage of the word "epigenetics" was employed by the psychologist Erik Erikson, who developed an "epigenetic theory of human development," which focuses on psycho-social crises. This article needs additional references or sources for verification. ...


The modern usage of the word "epigenetic" is usually more narrow, referring to heritable traits (over rounds of cell division and sometimes transgenerationally) that do not involve changes to the underlying DNA sequence.[8] The Greek prefix "epi-" in the word "epigenetics" implies features that are "on top of" or "in addition to" genetics, and the current usage of the word reflects this—epigenetic traits exist on top of or in addition to the traditional molecular basis for inheritance.


The similarity of the word to "genetics" has generated many parallel usages. The "epigenome" is a parallel to the word "genome," and refers to the overall epigenetic state of a cell. The phrase "genetic code" has also been adapted—the "epigenetic code" has been used to describe the set of epigenetic features that create different phenotypes in different cells. Taken to its extreme, the "epigenetic code" could represent the total state of the cell, with the position of each molecule accounted for; more typically, the term is used in reference to systematic efforts to measure specific, relevant forms of epigenetic information such as the histone code or DNA methylation patterns. 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). ... For a non-technical introduction to the topic, see Introduction to Genetics. ... The epigenetic code is hypothesized to be a defining code in every eukaryotic cell consisting of the specific epigenetic modification in each cell. ... The Histone Code is hypothesized to be a code consisting of covalent histone tail modifications. ... DNA methylation is a type of chemical modification of DNA that can be inherited without changing the DNA sequence. ...


Mechanisms

Several types of epigenetic inheritance systems may play a role in what has become known as cell memory:[9]


DNA methylation and chromatin remodeling

DNA associates with histone proteins to form chromatin.

Because the phenotype of a cell or individual is affected by which of its genes are transcribed, heritable transcription states can give rise to epigenetic effects. There are several layers of regulation of gene expression, one of which is remodeling of chromatin, the complex of DNA and the histone proteins with which it associates. Chromatin remodeling is initiated by one of two things: Image File history File links Download high-resolution version (1024x1024, 1067 KB) By Richard Wheeler (Zephyris) 2005; Nucleosome structure. ... Image File history File links Download high-resolution version (1024x1024, 1067 KB) By Richard Wheeler (Zephyris) 2005; Nucleosome structure. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... 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... Schematic representation of the assembly of the core histones into the nucleosome. ...

  1. posttranslational modification of the amino acids that make up histone proteins,
  2. or the addition of methyl groups to the DNA, at CpG sites, to convert cytosine to 5-methylcytosine.

Whereas DNA is not completely stripped of nucleosomes during replication, it is possible that the remaining modified histones may act as templates, initiating identical modification of surrounding new histones after deposition. DNA methylation has a more clear method of propagation through the preferential methylation of hemimethylated symmetric sites by enzymes like Dnmt 1. Posttranslational modification is the chemical modification of a protein after its translation. ... cytosine phosphate guanine CpG sites are regions of DNA where a cytosine nucleotide occurs next to a guanine nucleotide in the linear sequence of bases along its length. ... 5-methylcytosine is the methylated form of cytosine. ... A nucleosome is a unit made of DNA and histones. ...


Although modifications occur throughout the histone sequence, the unstructured termini of histones (called histone tails) are particularly highly modified. These modifications include acetylation, methylation and ubiquitylation. Acetylation is the most highly studied of these modifications. For example, acetylation of the K14 and K9 lysines of the tail of histone H3 by histone acetyltransferase enzymes (HATs) is generally correlated with transcriptional competence. Acetylation describes a reaction, usually with acetic acid, that introduces an acetyl functional group into an organic compound. ... Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. ... Ribbon representation of ubiquitin. ... Lysine is one of the 20 amino acids normally found in proteins. ...


One mode of thinking is that this tendency of acetylation to be associated with "active" transcription is biophysical in nature. Because lysine normally has a positive charge on the nitrogen at its end, lysine can bind the negatively charged phosphates of the DNA backbone and prevent them from repelling each other. The acetylation event converts the positively charged amine group on the side chain into a neutral amide linkage. This removes the positive charge causing the DNA to repel itself. When this occurs, complexes like SWI/SNF and other transcriptional factors can bind to the DNA, thus opening it up and exposing it to enzymes like RNA polymerase so transcription of the gene can occur. This article does not cite any references or sources. ...


In addition, the positively charged tails of histone proteins from one nucleosome may interact with the histone proteins on a neighboring nucleosome, causing them to pack closely. Lysine acetylation may interfere with these interactions, causing the chromatin structure to open up.


Lysine acetylation may also act as a beacon to recruit other activating chromatin modifying enzymes (and basal transcription machinery as well). Indeed, the bromodomain—a protein segment (domain) that specifically binds acetyl-lysine—is found in many enzymes that help activate transcription including the SWI/SNF complex (on the protein polybromo). It may be that acetylation acts in this and the previous way to aid in transcriptional activation.


The idea that modifications act as docking modules for related factors is borne out by histone methylation as well. Methylation of lysine 9 of histone H3 has long been associated with constitutively transcriptionally silent chromatin (constitutive heterochromatin). It has been determined that a chromodomain (a domain that specifically binds methyl-lysine) in the transcriptionally repressive protein HP1 recruits HP1 to K9 methylated regions. One example that seems to refute the biophysical model for acetylation is that tri-methylation of histone H3 at lysine 4 is strongly associated with (and required for full) transcriptional activation. Tri-methylation in this case would introduce a fixed positive charge on the tail. For differently-colored eyes, see Heterochromia. ... The family of Heterochromatin Protein 1 (HP1) (Chromobox Homolog, CBX) are highly conserved adapter molecules, which have an important function in the cell nucleus. ...


It should be emphasized that differing histone modifications are likely to function in differing ways; acetylation at one position is likely to function differently than acetylation at another position. Also, multiple modifications may occur at the same time, and these modifications may work together to change the behavior of the nucleosome. The idea that multiple dynamic modifications regulate gene transcription in a systematic and reproducible way is called the histone code. The Histone Code is hypothesized to be a code consisting of covalent histone tail modifications. ...


DNA methylation frequently occurs in repeated sequences, and may help to suppress 'junk DNA':[10] Because 5-methylcytosine is chemically very similar to thymidine, CpG sites are frequently mutated and become rare in the genome, except at CpG islands where they remain unmethylated. Epigenetic changes of this type thus have the potential to direct increased frequencies of permanent genetic mutation. DNA methylation patterns are known to be established and modified in response to environmental factors by a complex interplay of at least three independent DNA methyltransferases, DNMT1, DNMT3A and DNMT3B, the loss of any of which is lethal in mice.[11] DNMT1 is the most abundant methyltransferase in somatic cells,[12] localizes to replication foci,[13] has a 10–40-fold preference for hemimethylated DNA and interacts with the proliferating cell nuclear antigen (PCNA).[14] By preferentially modifying hemimethylated DNA, DNMT1 transfers patterns of methylation to a newly synthesized strand after DNA replication, and therefore is often referred to as the ‘maintenance' methyltransferase.[15] DNMT1 is essential for proper embryonic development, imprinting and X-inactivation.[11][16] In molecular biology, junk DNA is a collective label for the portions of the DNA sequence of a chromosome or a genome for which no function has yet been identified. ... 5-methylcytosine is the methylated form of cytosine. ... The chemical structure of deoxythymidine Thymidine (more precisely called deoxythymidine can also be labelled deoxyribosylthymine, and thymine deoxyriboside) is a chemical compound, more precisely a pyrimidine deoxynucleoside. ... CpG islands are small stretches of DNA rich in CG doublets found near the 5 regions of some genes. ... DNA methylation is a type of chemical modification of DNA that can be inherited without changing the DNA sequence. ... DNA methyltransferase is an enzyme whose function is to catalyze the transfer of methyl groups between molecules, in this case, DNA. There are two main types of methyltransferases, de novo and maintenance. ... DNA replication. ...


Chromosomal regions can adopt stable and heritable alternative states resulting in bistable gene expression without changes to the DNA sequence. Epigenetic control is often associated with alternative covalent modifications of histones. The stability and heritability of states of larger chromosomal regions are often thought to involve positive feedback where modified nucleosomes recruit enzymes that similarly modify nearby nucleosomes. A simplified stochastic model for this type of epigenetics is found here [17] .


Because DNA methylation and chromatin remodeling play such a central role in many types of epigenic inheritance, the word "epigenetics" is sometimes used as a synonym for these processes. However, this can be misleading. Chromatin remodeling is not always inherited, and not all epigenetic inheritance involves chromatin remodeling.[18]


It has been suggested that the histone code could be mediated by the effect of small RNAs. The recent discovery and characterization of a vast array of small (21- to 26-nt), non-coding RNAs suggests that there is an RNA component, possibly involved in epigenetic gene regulation. Small interfering RNAs can modulate transcriptional gene expression via epigenetic modulation of targeted promoters.[19] The Histone Code is hypothesized to be a code consisting of covalent histone tail modifications. ... A promoter is a regulatory region of DNA located upstream (towards the 5 region) of a gene, providing a control point for regulated gene transcription. ...


RNA transcripts and their encoded proteins

Sometimes a gene, after being turned on, transcribes a product that (either directly or indirectly) maintains the activity of that gene. For example, Hnf4 and MyoD enhance the transcription of many liver- and muscle-specific genes, respectively, including their own, through the transcription factor activity of the proteins they encode. Other epigenetic changes are mediated by the production of different splice forms of RNA, or by formation of double-stranded RNA (RNAi). Descendants of the cell in which the gene was turned on will inherit this activity, even if the original stimulus for gene-activation is no longer present. These genes are most often turned on or off by signal transduction, although in some systems where syncytia or gap junctions are important, RNA may spread directly to other cells or nuclei by diffusion. A large amount of RNA and protein is contributed to the zygote by the mother during oogenesis or via nurse cells, resulting in maternal effect phenotypes. A smaller quantity of sperm RNA is transmitted from the father, but there is recent evidence that this epigenetic information can lead to visible changes in several generations of offspring.[20] HNF4 is a protein mostly found in the liver. ... MyoD is a gene the helps control muscle differentiation. ... 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. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... In genetics, splicing is a modification of genetic information after transcription, in which introns of precursor messenger RNA (pre-mRNA) are removed and exons of it are joined. ... For other uses, see RNA (disambiguation). ... In molecular biology, RNA interference (RNAi) is a mechanism in which the presence of small fragments of double-stranded RNA (dsRNA) whose sequence matches a given gene interferes with the expression of that gene. ... In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in what is thought of as... In biology, a syncytium is a large region of cytoplasm that contains many nuclei. ... gap junction A gap junction is a junction between certain animal cell-types that allows different molecules and ions to pass freely between cells. ... diffusion (disambiguation). ... For other meanings see Zygote (disambiguation). ... Oogenesis or rarely oögenesis is the creation of an ovum (egg cell). ... Nurse cell is a term used to describe a process in the disease trichinosis, in which a trichinella larvae takes up residence in a cell. ... A maternal effect, in genetics, is the phenomena where the genotype of a mother is expressed in the phenotype of its offspring. ...


Prions

For more details on this topic, see Prions.

Prions are infectious forms of proteins. Proteins generally fold into discrete units which perform distinct cellular functions, but some proteins are also capable of forming an infectious conformational state known as a prion. Although often viewed in the context of infectious disease, prions are more loosely defined by their ability to catalytically convert other native state versions of the same protein to an infectious conformational state. It is in this latter sense that they can be viewed as epigenetic agents capable of inducing a phenotypic change without a modification of the genome.[21] For the bird called a prion, see Prion (bird) Prions - short for proteinaceous infectious particle - are infectious self-reproducing protein structures. ... For the bird, see Prion (bird). ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Transmissible spongiform encephalopathies (TSEs, also known as prion diseases) are a group of progressive conditions that affect the brain and nervous system of humans and animals and are transmitted by prions. ...


Fungal prions are considered epigenetic because the infectious phenotype caused by the prion can be inherited without modification of the genome. PSI+ and URE3, discovered in yeast in 1965 and 1971, are the two best studied of this type of prion.[22][23] Prions can have a phenotypic effect through the sequestration of protein in aggregates, thereby reducing that protein's activity. In PSI+ cells, the loss of the Sup35 protein (which is involved in termination of translation) causes ribosomes to have a higher rate of read-through of stop codons, an effect which results in suppression of nonsense mutations in other genes.[24] The ability of Sup35 to form prions may be a conserved trait. It could confer an adaptive advantage by giving cells the ability to switch into a PSI+ state and express dormant genetic features normally terminated by premature stop codon mutations.[25][26] It has been suggested that this article or section be merged with PSI (prion). ... It has been suggested that this article or section be merged with Fungal prions. ... Binomial name Meyen ex E.C. Hansen Saccharomyces cerevisiae is a species of budding yeast. ... In genetics, a nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon (also called a nonsense codon) in the transcribed mRNA, and possibly a truncated (and often nonfunctional) protein product. ...


Structural inheritance systems

For more details on this topic, see Structural inheritance.

In ciliates such as Tetrahymena and Paramecium, genetically identical cells show heritable differences in the patterns of ciliary rows on their cell surface. Experimentally altered patterns can be transmitted to daughter cells. It seems existing structures act as templates for new structures. The mechanisms of such inheritance are unclear, but reasons exist to assume that multicellular organisms also use existing cell structures to assemble new ones.[27] Structural inheritance is the transmission of a trait in a living organism by a self-perpetuating spatial structures. ... Classes Karyorelictea Heterotrichea Spirotrichea Litostomatea Phyllopharyngea Nassophorea Colpodea Prostomatea Oligohymenophorea Plagiopylea See text for subclasses. ... Species T hegewischi Tetrahymena are non-pathogenic free-living ciliate protozoa. ... Species Paramecium tetraurelia Paramecium aurelia Paramecium caudatum The Paramecium is a group of unicellular ciliate protozoa formerly known as slipper animalcules from their slipper shape. ...


Functions and consequences

Development

Somatic epigenetic inheritance, particularly through DNA methylation and chromatin remodeling, is very important in the development of multicellular eukaryotic organisms. The genome sequence is static (with some notable exceptions), but cells differentiate in many different types, which perform different functions, and respond differently to the environment and intercellular signalling. Thus, as individuals develop, morphogens activate or silence genes in an epigenetically heritable fashion, giving cells a "memory". In mammals, most cells terminally differentiate, with only stem cells retaining the ability to differentiate into several cell types ("totipotency" and "multipotency"). In mammals, some stem cells continue producing new differentiated cells throughout life, but mammals are not able to respond to loss of some tissues, for example, the inability to regenerate limbs, which some other animals are capable of. Unlike animals, plant cells do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. While plants do utilise many of the same epigenetic mechanisms as animals, such as chromatin remodeling, it has been hypothesised that plant cells do not have "memories", resetting their gene expression patterns at each cell division using positional information from the environment and surrounding cells to determine their fate.[28] A morphogen is a substance governing the pattern of tissue development and, in particular, the positions of the various specialized cell types within a tissue. ... Mouse embryonic stem cells. ...


Medicine

Epigenetics has many and varied potential medical applications. Congenital genetic disease is well understood, and it is also clear that epigenetics can play a role, for example, in the case of Angelman syndrome and Prader-Willi syndrome. These are normal genetic diseases caused by gene deletions, but are unusually common because individuals are essentially hemizygous because of genomic imprinting, and therefore a single gene knock out is sufficient to cause the disease, where most cases would require both copies to be knocked out.[29] Angelman syndrome (AS) is a rare neuro-genetic disorder named after a British pediatrician, Dr. Harry Angelman, who first described the syndrome in 1965. ... -1... Hemizygous describes an diploid individual who has only one allele of a gene or chromosome segment rather than the usual two. ... Genomic imprinting is a genetic phenomenon involved in the control of a small proportion of genes in the genome, where the allele that is expressed is determined solely on which parent contributes it. ...


Evolution

Although epigenetics in multicellular organisms is generally thought to be a mechanism involved in differentiation, with epigenetic patterns "reset" when organisms reproduce, there have been some observations of transgenerational epigenetic inheritance (e.g., the phenomenon of paramutation observed in maize). Although most of these multigenerational epigenetic traits are gradually lost over several generations, the possibility remains that multigenerational epigenetics could be another aspect to evolution and adaptation. These effects may require enhancements to the standard conceptual framework of the modern evolutionary synthesis.[30][31] Paramutation, in genetics, is an interaction between two alleles of a single locus, resulting in a heritable change of one allele. ... The modern evolutionary synthesis refers to a set of ideas from several biological specialities that were brought together to form a unified theory of evolution accepted by the great majority of working biologists. ...


Epigenetic features may play a role in short-term adaptation of species by allowing for reversible phenotype variability. The modification of epigenetic features associated with a region of DNA allows organisms, on a multigenerational time scale, to switch between phenotypes that express and repress that particular gene.[32] Whereas the DNA sequence of the region is not mutated, this change is reversible. It has also been speculated that organisms may take advantage of differential mutation rates associated with epigenetic features to control the mutation rates of particular genes.[32]


Epigenetic changes have also been observed to occur in response to environmental exposure—for example, mice given some dietary supplements have epigenetic changes affecting expression of the agouti gene, which affects their fur color, weight, and propensity to develop cancer.[33][34] The genetics of cat coat length and coloration is a complex subject, and many different genes are involved. ...


Epigenetic effects in humans

Genomic imprinting and related disorders

Some human disorders are associated with genomic imprinting, a phenomenon in mammals where the father and mother contribute different epigenetic patterns for specific genomic loci in their germ cells.[35] The most well-known case of imprinting in human disorders is that of Angelman syndrome and Prader-Willi syndrome—both can be produced by the same genetic mutation, chromosome 15q partial deletion, and the particular syndrome that will develop depends on whether the mutation is inherited from the child's mother or from their father.[36] This is due to the presence of genomic imprinting in the region. Beckwith-Wiedemann syndrome is also associated with genomic imprinting, often caused by abnormalities in maternal genomic imprinting of a region on chromosome 11. Angelman syndrome (AS) is a rare neuro-genetic disorder named after a British pediatrician, Dr. Harry Angelman, who first described the syndrome in 1965. ... -1... Chromosome 15q partial deletion is an extremely rare genetic disorder, caused by a chromosomal aberration in which one of the long (q) arms of human chromosome 15 is deleted. ... Genomic imprinting is a genetic phenomenon involved in the control of a small proportion of genes in the genome, where the allele that is expressed is determined solely on which parent contributes it. ... Beckwith-Wiedemann syndrome (BWS) is a very rare genetic overgrowth syndrome (prevalence of about 1 in 36,000). ...


Transgenerational epigenetic observations

Marcus Pembrey and colleagues also observed that the paternal (but not maternal) grandsons of Swedish boys who were exposed to famine in the 19th century were less likely to die of cardiovascular disease; if food was plentiful then diabetes mortality in the grandchildren increased, suggesting that this was a transgenerational epigenetic inheritance.[37] This article is about the disease that features high blood sugar. ...


Cancer and developmental abnormalities

A variety of compounds are considered as epigenetic carcinogens—they result in an increased incidence of tumors, but they do not show mutagen activity (toxic compounds or pathogens that cause tumors incident to increased regeneration should also be excluded). Examples include diethylstilbestrol, arsenite, hexachlorobenzene, and nickel compounds. In pathology, a carcinogen is any substance or agent that promotes cancer. ... 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. ... Diethylstilbestrol (DES) is a drug, a synthetic nonsteroidal estrogen that was first synthesized in 1938. ... The arsenite ion is H2AsO3−, or similar. ... Hexachlorobenzene(or perchlorobenzene)is a chlorinated hydrocarbon fungicide used as a seed treatment, especially on wheat. ... For other uses, see Nickel (disambiguation). ...


Many teratogens exert specific effects on the fetus by epigenetic mechanisms.[38][39] While epigenetic effects may preserve the effect of a teratogen such as diethylstilbestrol throughout the life of an affected child, the possibility of birth defects resulting from exposure of fathers or in second and succeeding generations of offspring has generally been rejected on theoretical grounds and for lack of evidence.[40] However, a range of male-mediated abnormalities have been demonstrated, and more are likely to exist.[41] FDA label information for Vidaza(tm), a formulation of 5-azacitidine (an unmethylatable analog of cytidine that causes hypomethylation when incorporated into DNA) states that "men should be advised not to father a child" while using the drug, citing evidence in treated male mice of reduced fertility, increased embryo loss, and abnormal embryo development. In rats, endocrine differences were observed in offspring of males exposed to morphine.[42] In mice, second generation effects of diethylstilbesterol have been described occurring by epigenetic mechanisms.[43] Diethylstilbestrol (DES) is a drug, a synthetic nonsteroidal estrogen that was first synthesized in 1938. ... 5-Azacytidine is a chemical analogue of the cytosine nucleoside used in DNA and RNA. Cells in the presence of 5-azacytidine incorporate it into DNA during transcription and RNA during translation. ...


Epigenetics in microorganisms

Bacteria make widespread use of postreplicative DNA methylation for the epigenetic control of DNA-protein interactions. Bacteria make use of DNA adenine methylation (rather than DNA cytosine methylation) as an epigenetic signal. DNA adenine methylation is important in bacteria virulence in organisms such as Escherichia coli, Salmonella, Vibrio, Yersinia, Haemophilus, and Brucella. In Alphaproteobacteria, methylation of adenine regulates the cell cycle and couples gene transcription to DNA replication. In Gammaproteobacteria, adenine methylation provides signals for DNA replication, chromosome segregation, mismatch repair, packaging of bacteriophage, transposase activity and regulation of gene expression.[44] [45] E. coli redirects here. ... Species S. bongori S. enterica This article is about the bacteria. ... Vibrio is a genus of bacteria, included in the gamma subgroup of the Proteobacteria. ... Species Y. pestis Y. enterocolitica Y. pseudotuberculosis etc. ... Species H. ducreyi H. influenzae etc. ... Species B. abortus B. melitensis Brucella is a genus of Gram-negative bacteria. ... Orders Alpha Proteobacteria    Caulobacterales - e. ...


The yeast prion PSI is generated by a conformational change of a translation termination factor, which is then inherited by daughter cells. This can provide a survival advantage under adverse conditions. This is an example of epigenetic regulation enabling unicellular organisms to respond rapidly to environmental stress. Prions can be viewed as epigenetic agents capable of inducing a phenotypic change without modification of the genome.[45] Typical divisions Ascomycota (sac fungi) Saccharomycotina (true yeasts) Taphrinomycotina Schizosaccharomycetes (fission yeasts) Basidiomycota (club fungi) Urediniomycetes Sporidiales Yeasts are a growth form of eukaryotic micro organisms classified in the kingdom Fungi, with about 1,500 species described;[1] they dominate fungal diversity in the oceans. ... For the bird, see Prion (bird). ...


See also

The Histone Code is hypothesized to be a code consisting of covalent histone tail modifications. ... Baldwinian evolution is a theory proposed by United States psychologist James Mark Baldwin which states that organisms can pass on learned abilities to their offspring. ... Barbara McClintock (June 16, 1902 – September 2, 1992) was a pioneering American scientist and one of the worlds most distinguished cytogeneticists. ... Chromosome. ... Evolutionary developmental psychology, (or EDP), is the application of the basic principles of Darwinian evolution, particularly natural selection, to explain contemporary human development. ... Molecular biology is the study of biology at a molecular level. ... A somatic epitype is a non-heritable epigenetic alteration in a gene. ... The Weismann barrier is the principle that hereditary information moves only from genes to body cells but never in reverse. ...

Further reading

  • Oskar Hertwig, 1849-1922. Biological problem of today: preformation or epigenesis? The basis of a theory of organic development. W. Heinemann: London, 1896.
  • R. Jaenisch and A. Bird (2003) Epigenetic regulation of gene expression: how the genome integrates intrinsic and environmental signals. Nat. Genet. 33 (Suppl) 245-254.
  • Joshua Lederberg, "The Meaning of Epigenetics", The Scientist 15(18):6, Sep. 17, 2001.
  • R. J. Sims III, K. Nishioka and D. Reinberg (2003) Histone lysine methylation: a signature for chromatin function. Trends Genet. 19, 629-637.
  • Rupert Sheldrake, A New Biology, morphogenetic fields.
  • B. D. Strahl and C. D. Allis (2000) The language of covalent histone modifications. Nature 403, 41-45.
  • C.H. Waddington (1942), "The epigenotype". Endeavour 1, 18–20.
  • B. McClintock (1978) Mechanisms that Rapidly Reorganize the Genome. Stadler Symposium vol 10:25-48
  • G.W. Grimes; K.J. Aufderheide; Cellular Aspects of Pattern Formation: the Problem of Assembly. Monographs in Developmental Biology, Vol. 22. Karger, Basel (1991)
  • Eva Jablonka and Marion J. Lamb Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life The MIT Press (2005) ISBN 978-0262101073
  • Article on The Philosophy of Molecular and Developmental Biology to appear in Blackwell’s Guide to Philosophy of Science,. P.K. Machamer and M. Silberstein (Eds).
  • Epigenetics edited by C. David Allis, Thomas Jenuwein, Danny Reinberg, and Marie-Laure Caparros. Cold Spring Harbor Press, 2007.
  • Evolution by Nicholas Barton, Derek Briggs, Jonathan Eisen, David Goldstein, and Nipam Patel. Cold Spring Harbor Press, 2007.
  • Chromatin and Gene Regulation: Mechanisms in Epigenetics by Bryan Turner. Blackwell Publishing, 2002.
  • Survival of the Sickest by Sharon Moalem with Jonathan Prince, Published 2007
  • Epigenetics edited by J. Tost. Caister Academic Press, 2008.
  • RNA and the Regulation of Gene Expression: A Hidden Layer of Complexity edited by K. V. Morris. Caister Academic Press, 2008.

Oskar Hertwig (April 21, 1849, Friedberg, Hessen - October 25, 1922, Berlin) was a German zoologist. ... Joshua Lederberg speaking at a conference in 1997 Joshua Lederberg (born May 23, 1925) is an American molecular biologist who is known for his work in genetics, artificial intelligence, and space exploration. ... Conrad Hal Waddington (1905 — 1975) was a biologist, paleontologist, embryologist and philosopher. ... Eva Jablonka - born 1944 - publishes about evolutionary themes. ... This article is about evolution in biology. ...

Notes and references

  1. ^ Adrian Bird (2007). "Perceptions of epigenetics". Nature 447: 396–398. doi:10.1038/nature05913.  PMID 17522671
  2. ^ Special report: 'What genes remember' by Philip Hunter | Prospect Magazine May 2008 issue 146
  3. ^ Reik, Wolf (2007-05-23). "Stability and flexibility of epigenetic gene regulation in mammalian development". Nature 447 (May (online)): 425-432. doi:10.1038/nature05918. Retrieved on 2008-04-05. 
  4. ^ V.L. Chandler (2007). "Paramutation: From Maize to Mice". Cell 128: 641–645. doi:10.1016/j.cell.2007.02.007. 
  5. ^ Roloff, T.C., Nuber, U.A., 2005 Chromatin , epigenetics and stem cells. Eur J Cell Biol. 84, 123-135
  6. ^ C.H. Waddington (1942). "The epigenotype". Endeavour 1: 18–20. 
  7. ^ Holliday, R., 1990. Mechanisms for the control of gene activity during development. Biol. Rev. Cambr. Philos. Soc. 65, 431-471
  8. ^ Russo, V.E.A., Martienssen, R.A., Riggs, A.D., 1996 Epigenetic mechanisms of gene regulation. Cold Spring Harbor Laboratory Press, Plainview, NY.
  9. ^ Jablonka, E; Lamb MJ and Lachmann M (September 1992). "Evidence, mechanisms and models for the inheritance of acquired characteristics". J. Theoret. Biol. 158 (2): 245–268. doi:10.1016/S0022-5193(05)80722-2. 
  10. ^ Chédin, F (1992). "The Chedin Laboratory". Retrieved on 2006-12-28.
  11. ^ a b Li, E; Bestor TH and Jaenisch R (June 1992). "Targeted mutation of the DNA methyltransferase gene results in embryonic lethality". Cell 69 (6): 915–926. doi:10.1016/0092-8674(92)90611-F. 
  12. ^ Robertson, KD; Uzyolgi E, Lian G et al (June 1999). "The human DNA methyltransferases (DNMTs) 1, 3a, 3b: Coordinate mRNA expression in normal tissues and overexpression in tumors". Nucleic Acids Res 27 (11): 2291–2298. doi:10.1093/nar/27.11.2291. PMID 10325416. 
  13. ^ Leonhardt, H; Page AW, Weier HU, Bestor TH (November 1992). "A targeting sequence directs DNA methyltransferase to sites of DNA replication in mammalian nuclei". Cell 71 (5): 865–873. doi:10.1016/0092-8674(92)90561-P. 
  14. ^ Chuang, LS; Ian HI, Koh TW et al (September 1997). "Human DNA-(cytosine-5) methyltransferase-PCNA complex as a target for p21WAF1". Science 277 (5334): 1996–2000. doi:10.1126/science.277.5334.1996. PMID 9302295. 
  15. ^ Robertson, KD; Wolffe AP (October 2000). "DNA methylation in health and disease". Nat Rev Genet 1 (1): 11–19. doi:10.1038/35049533. 
  16. ^ Li, E; Beard C and Jaenisch R (December 1993). "Role for DNA methylation in genomic imprinting". Nature 366 (6453): 362–365. doi:10.1038/366362a0. 
  17. ^ I.B. Dodd, M.A. Micheelsen, K. Sneppen and G. Thon (2007). Theoretical Analysis of Epigenetic Cell Memory by Nucleosome Modification Cell 129:813-822.
  18. ^ Mark Ptashne, 2007. On the use of the word ‘epigenetic’. Current Biology, 17(7):R233-R236. doi:10.1016/j.cub.2007.02.030
  19. ^ Morris KV (2008). "Epigenetic Regulation of Gene Expression", RNA and the Regulation of Gene Expression: A Hidden Layer of Complexity. Caister Academic Press. ISBN 978-1-904455-25-7. 
  20. ^ Choi CQ (2006-05-25). "The Scientist: RNA can be hereditary molecule". The Scientist. Retrieved on 2006.
  21. ^ A. Yool and W.J. Edmunds (1998). "Epigenetic inheritance and prions". Journal of Evolutionary Biology 11: 241–242. doi:10.1007/s000360050085. 
  22. ^ B.S. Cox (1965). "[PSI], a cytoplasmic suppressor of super-suppression in yeast". Heredity 20: 505–521. doi:10.1038/hdy.1965.65. 
  23. ^ F. Lacroute (1971). "Non-Mendelian mutation allowing ureidosuccinic acid uptake in yeast". Journal of Bacteriology 106: 519–522. 
  24. ^ S.W. Liebman and F. Sherman (1979). "Extrachromosomal psi+ determinant suppresses nonsense mutations in yeast". Journal of Bacteriology 139 (3): 1068–1071.  Free full text available
  25. ^ H.L. True and S.L. Lindquist (2000). "A yeast prion provides a mechanism for genetic variation and phenotypic diversity". Nature 407: 477–483. doi:10.1038/35035005. 
  26. ^ J. Shorter and S. Lindquist (2005). "Prions as adaptive conduits of memory and inheritance". Nature Reviews Genetics 6 (6): 435–450. doi:10.1038/nrg1616. 
  27. ^ Oyama, Susan; Paul E. Griffiths, Russell D. Gray (2001). Cycles of Contingency: Developmental Systems and Evolution. MIT Press. ISBN 0262650630. 
  28. ^ Silvia Costa and Peter Shaw. 2006. 'Open Minded' cells: how cells can change fate. Trends in Cell Biology 17(3):101-106. doi:10.1016/j.tcb.2006.12.005
  29. ^ Online 'Mendelian Inheritance in Man' (OMIM) 105830
  30. ^ Jablonka, Eva; Marion J. Lamb (2005). Evolution in Four Dimensions. MIT Press. ISBN 0-262-10107-6. 
  31. ^ See also Denis Noble The Music of Life see esp pp93-8 and p48 where he cites Jablonka & Lamb and Massimo Pigliucci's review of Jablonka and Lamb in Nature 435, 565-566 (2 June 2005)
  32. ^ a b O.J. Rando and K.J. Verstrepen (2007). "Timescales of Genetic and Epigenetic Inheritance". Cell 128: 655–668. doi:10.1016/j.cell.2007.01.023. 
  33. ^ Cooney, CA, Dave, AA, and Wolff, GL (2002). "Maternal Methyl Supplements in Mice Affect Epigenetic Variation and DNA Methylation of Offspring". Journal of Nutrition 132: 2393S–2400S. available online
  34. ^ Waterland RA and Jirtle RL (August 2003). "Transposable elements: Targets for early nutritional effects on epigenetic gene regulation". Molecular and Cellular Biology 23 (15): 5293–5300. doi:10.1128/MCB.23.15.5293-5300.2003. PMID 12861015. 
  35. ^ A.J. Wood and A.J. Oakey (2006). "Genomic imprinting in mammals: Emerging themes and established theories". PLOS Genetics 2 (11): 1677–1685. doi:10.1371/journal.pgen.0020147.  available online
  36. ^ J.H.M. Knoll, R.D. Nicholls, R.E. Magenis, J.M. Graham Jr, M. Lalande, S.A. Latt (1989). "Angelman and Prader-Willi syndromes share a common chromosome deletion but differ in parental origin of the deletion". American Journal of Medical Genetics 32: 285–290. doi:10.1002/ajmg.1320320235. 
  37. ^ Pembrey ME, Bygren LO, Kaati G, et al. Sex-specific, male-line transgenerational responses in humans. Eur J Hum Genet 2006; 14: 159-66. PMID 16391557. Robert Winston refers to this study in a lecture; see also discussion at Leeds University, here
  38. ^ Bishop, JB; Witt KL and Sloane RA (December 1997). "Genetic toxiticities of human teratogens". Mutat Res 396 (1-2): 9–43. 
  39. ^ Gurvich, N; Berman MG, Wittner BS et al (July 2004). "Association of valproate-induced teratogenesis with histone deacetylase inhibition in vivo". FASEB J 19 (9): 1166–1168. doi:10.1096/fj.04-3425fje. PMID 15901671. 
  40. ^ Smithells, D (November 1998). "Does thalidomide cause second generation birth defects?". Drug Saf 19 (5): 339–341. doi:10.2165/00002018-199819050-00001. 
  41. ^ Friedler, G (December 1996). "Paternal exposures: impact on reproductive and developmental outcome. An overview.". Pharmacol Biochem Behav 55 (4): 691–700. doi:10.1016/S0091-3057(96)00286-9. 
  42. ^ Cicero, TJ; Adams NL, Giodarno A et al (March 1991). "Influence of morphine exposure during adolescence on the sexual maturation of male rats and the development of their offspring". J Pharmacol Exp Ther. 256 (3): 1086–1093. 
  43. ^ Newbold, RR; Padilla-Banks E and Jefferson WN (June 2006). "Adverse effects of the model environmental estrogen diethylstilbestrol are transmitted to subsequent generations". Endocrinology 147 (6 Suppl): S11–S17. doi:10.1210/en.2005-1164. PMID 16690809. 
  44. ^ Casadesus J and Low D (September 2006). "Epigenetic Gene Regulation in the Bacterial World". Microbiol Mol Biol Rev 70 (3): 830–856. doi:10.1128/MMBR.00016-06. 
  45. ^ a b Tost J (editor). (2008). Epigenetics. Caister Academic Press. ISBN 978-1-904455-23-3 . 

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. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 95th day of the year (96th 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. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 362nd day of the year (363rd 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. ... 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. ... 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. ... 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 145th day of the year (146th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of 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. ... 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. ... 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 Mendelian Inheritance in Man project is a database that catalogues all the known diseases with a genetic component, and - when possible - links them to the relevant genes in the human genome. ... Eva Jablonka - born 1944 - publishes about evolutionary themes. ... This article or section does not cite its references or sources. ... Dr. Massimo Pigliucci received his doctorate in genetics at the University of Ferrara, Italy, and PhD in botany from the University of Connecticut. ... Nature is a prominent scientific journal, first published on 4 November 1869. ... 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. ... 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. ... Professor Robert Winston Robert Maurice Lipson Winston, Baron Winston (born July 15, 1940) is a British scientist, politician, and television presenter. ... University Tower, University of Leeds The University of Leeds (United Kingdom) is amongst the largest of British universities and the most popular by applicants, with 52,444 applicants in 2003 for 7,228 places (UCAS). ... 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. ... 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. ... 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. ...

External links

  • DNA Is Not Destiny - Discover Magazine cover story
  • BBC - Horizon - 2005 - The Ghost In Your Genes
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. ... 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. ... In genetics, dominance describes a specific relationship between the effects of different versions of a gene (alleles) on a trait (phenotype). ... 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. ... 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 — 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. ... Molecular biology is the study of biology at a molecular level. ... 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... DNA replication. ... 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 micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. ... For other uses, see RNA (disambiguation). ... Translation is the second stage of protein biosynthesis (part of the overall process of gene expression). ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Gene modulation redirects here. ... Gene regulation is the general term for cellular control of protein synthesis at the DNA-RNA transcription step. ... Mitosis divides genetic information during cell division. ... It has been suggested that this article or section be merged into signal transduction. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Posttranslational modification means the chemical modification of a protein after its translation. ... A dry lab is a laboratory where computational or applied mathematical analyses are done on a computer generated model to simulate a phenomenon in the physical realm whether it be a molecule changing quantum states, the event horizon of a black hole or anything that otherwise might be too cumbersome... Wet Laboratories are defined as laboratories where chemicals, drugs, or other material or biological matter are tested and analyzed requiring water, direct ventilation, and specialized piped utilities. ... Views of a Foetus in the Womb, Leonardo da Vinci, ca. ... The history of molecular biology begins in the 1930s with the convergence of various, previously distinct biological disciplines: biochemistry, genetics, microbiology, and virology. ... A promoter is a regulatory region of DNA located upstream (towards the 5 region) of a gene, providing a control point for regulated gene transcription. ... The Pribnow box (also known as the Pribnow-Schaller box) is the sequence TATAAT of six nucleotides (thymine-adenine-thymine-etc. ... A TATA box (also called Goldberg-Hogness box)[1] is a DNA sequence (Cis-regulatory element) found in the promoter region of most genes (it is considered to be the core promoter sequence) in eukaryotes [2]. It is the binding site of either transcription factors or histones (binding of a... An operon is a group of key nucleotide sequences including an operator, a common promoter, and one or more structural genes that are controlled as a unit to produce messenger RNA (mRNA). ... The lac operon is an operon required for the transport and metabolism of lactose in Escherichia coli and some other enteric bacteria. ... Trp operon is an anabolic operon which promotes the production of tryptophan in the absence of tryptophan in the environment. ... In genetics, a terminator marks the end of a gene on the DNA for transcription. ... In genetics, an enhancer is a short region of DNA that can be bound with proteins (namely, the trans-acting factors, much like a set of transcription factors) to enhance transcription levels of genes (hence the name) in a gene-cluster. ... A repressor is a DNA-binding protein that regulates the expression of one or more genes by decreasing the rate of transcription. ... Lac Repressor molecule more details. ... The trp (tryptophan) repressor is a 25 kD protein which regulates transcription of the tryptophan biosynthetic pathway in bacteria. ... In genetics a silencer is a DNA sequence capable of binding transcription regulation factors termed repressors. ... Histone methylation is the modification of the primary protein sequence of a histone protein by the addition of an methyl group. ... 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. ... 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. ... C57BL/6, often referred to as C57 black 6 or just black 6 is a common inbred strain of lab mouse. ... Protein methods are the techniques used to study proteins. ... The tone or style of this article or section may not be appropriate for Wikipedia. ... Example of an approximately 40,000 probe spotted oligo microarray with enlarged inset to show detail. ... Mass spectrometry (previously called mass spectroscopy (deprecated) or informally, mass-spec and MS) is an analytical technique that measures the mass-to-charge ratio of ions. ... This article is about the technology. ... Cell biology (also called cellular biology or formerly cytology, from the Greek kytos, container) is an academic discipline that studies cells. ... Wöhler observes the synthesis of urea. ... Computational biology is an interdisciplinary field that applies the techniques of computer science and applied mathematics to problems inspired by biology. ... See also: gene expression, List of Glossaries, List of Natural Sciences Glossaries A constitutive gene or constitutive expression describes a gene that is transcribed continually compared to a facultative gene which is only transcribed when needed. ... Academic organizations typically have a rather rigid set of ranks. ...

  Results from FactBites:
 
Epigenetics - Wikipedia, the free encyclopedia (2002 words)
Epigenetics is the study of reversible heritable changes in gene function that occur without a change in the sequence of nuclear DNA.
Epigenetic inheritance occurs in the development of multicellular organisms: dividing fibroblasts for instance give rise to new fibroblasts (rather than some other cell type) even though their genome is identical to that of all other cells.
Epigenetic inheritance systems (EISs) allow cells of different phenotype but identical genotype to transmit their phenotype to their offspring, even when the phenotype-inducing stimuli are absent, as is often the case.
Epigenetics (602 words)
epigenetics, which attempts to explain the mysterious inner layers of the genetic onion that may account for why identical twins aren’t exactly identical and other conundrums, including why some people are predisposed to mental illness while others are not.
Epigenetics delves deeper into the onion, involving "information stored in the proteins and chemicals that surround and stick to DNA." Methylation is a chemical process that, among other things, aids in the transcription of DNA to RNA and is believed to defend the genome against parasitic genetic elements called transpons.
In a 2003 pilot study, Dr Petronis and his colleagues investigated the epigenetic gene modification in a section of the dopamine 2 receptor genes in two pairs of identical twins, one pair with both partners having schizophrenia and the other having only one partner with the illness.
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