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Epigenetic inheritance is the transmission of information from a cell or multicellular organism to its descendants without that information being encoded in the nucleotide sequence of the gene. The study of epigenetic inheritance is known as epigenetics. Wikipedia does not have an article with this exact name. ... It has been suggested that this article or section be merged with Epigenetic inheritance. ... Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, and are sometimes called the building blocks of life. ... In biology and ecology, an organism (in Greek organon = instrument) is a complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... It has been suggested that this article or section be merged with Epigenetic inheritance. ...

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. Quantitative genetic studies in mammals and birds can reveal maternal effects, which is a form of epigenetic transmission, from one generation to the next. This was first observed in maize. Non-genetic paternal effects are rare. A fibroblast is a cell that makes the structural fibers and ground substance of connective tissue. ... A fibroblast is a cell that makes the structural fibers and ground substance of connective tissue. ... Orders Subclass Multituberculata (extinct) Plagiaulacida Cimolodonta Subclass Palaeoryctoides (extinct) Subclass Triconodonta (extinct) Subclass Eutheria (includes extinct ancestors)/Placentalia (excludes extinct ancestors) Afrosoricida Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Litopterna (extinct) Macroscelidea Mesonychia (extinct) Notoungulata (extinct) Perissodactyla Pholidota Plesiadapiformes... Orders Many - see section below. ... A maternal effect, in genetics, is the phenomena where the genotype of a mother is expressed in the phenotype of its offspring. ... Binomial name Zea mays L. Maize (Zea mays ssp. ...

Epigenetic inheritance systems

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. Jablonka et al. (ref. 2), name three types of EISs that may play a role in what has become known as cell memory. The phenotype of an individual organism is either its total physical appearance and constitution or a specific manifestation of a trait, such as size or eye color, that varies between individuals. ... The genotype is the specific genetic makeup (the specific genome) of an individual, usually in the form of DNA. It codes for the phenotype of that individual. ...

1. Steady-state systems. Some metabolic patterns are self-perpetuating. Sometimes a gene, after being turned on, transcribes a product (either directly or indirectly) that maintains the activity of that gene. 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. Also, diffusion of the gene's product to other cells can make the (heritable) characteristic spread.
2. Structural inheritance systems. 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. (ref. 3)
3. Chromatin-marking systems. Proteins or chemical groups that are attached to DNA and modify its activity are called chromatin marks. These marks are copied with the DNA. For example, several cytosines in eukaryotic DNA are methylated (5-methylcytosine). The number and pattern of such methylated cytosines influences the functional state of the gene: low levels of methylation correspond to high potential activity while high levels correspond to low activity. While there are random changes in the methylation pattern, there are also very specific ones, induced by environmental factors. After DNA replication, maintenance DNA methyltransferase make sure the methylation pattern of the parental DNA is copied to the daughter strand.

Structural inheritance is the transmission of a trait in a living organism by a self-perpetuating spatial structures. ... Classes & Subclasses Class Karyorelictea Class Heterotrichea (e. ... Species T hegewischi Tetrahymena are non-pathogenic free-living ciliate protozoa. ... Paramecium is a well-known genus of ciliate protozoa, commonly studied as a representative of that group. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (also spelled eucaryote) is an organism with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... 5-methylcytosine is the methylated form of cytosine. ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... DNA replication. ... 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. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ...

Comparison to standard theories

Epigenetic variants exhibit spontaneous emergence and reversion. However, they can be induced by the presence of other genetic factors, and some alleles of a gene have been shown to convert the epigenetic status of the same locus on the homologous chromosome. Environmental factors are also known to influence the emergence and reversion of epigenetic factors. This produces the possibility that epigenetic variations might be produced at several loci and in several cells or organisms.

Epigenetic coding and evolution

One question which is now raised is to what extent does epigenetic inheritance play a direct role in evolution? Since the discovery of the structure of DNA in the mid-20th century, biologists have held that the only role the environment plays is in the phase of selection: the environment determines on what grounds selection takes place and what characteristics are necessary for better reproduction opportunities. A speculatively rooted phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the three domains, bacteria, archaea, and eukaryotes, as described initially by Carl Woese. ...

For selection to be possible, individuals within a species must differ somewhat. Genes that provide characteristics that allow an organism to survive in its environment become more common over time, while genes that provide characteristics that make the organism less likely to survive become less common over time.

These genetic differences between individuals are thought to arise from random mutations, and in organisms that reproduce sexually, from meiosis. These differences physically exist as changes in the nucleotide base sequence of DNA. The environment can influence these variations. For example, radioactivity randomly changes the base sequence of DNA. In biology, meiosis is the process that transforms one diploid cell into four haploid cells in eukaryotes in order to redistribute the diploids cells genome. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ...

Some forms of epigenetic inheritance may be maintained even through the production of germ cells (meiosis). In biology, meiosis is the process that transforms one diploid cell into four haploid cells in eukaryotes in order to redistribute the diploids cells genome. ...

A number of experimental studies seem to indicate that epigenetic inheritance plays a part in the evolution of complex organisms. For example, Tremblay et al. (ref. 3), have shown that methylation differences between maternally and paternally inherited alleles of the mouse H19 gene are preserved. There are also numerous reports of heritable epigenetic marks in plants.

That epigenetic heredity seems to exist transgenerationally in complex organisms can be explained by allowing for minor epigenetic changes not affecting totipotency. This puts some constraints on the extent to which epigenetic changes can be brought upon DNA, but it allows for EISs to play direct evolutionary roles. 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. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and most viruses). ...

However, in none of these cases does a cell reprogram its DNA to produce genes that increase its ability to survive in a given environment.

Possible epigenetic effects in humans

Work by Marcus Pembrey indicates that both Angelman syndrome and Prader-Willi syndrome appear to be produced by the same genetic mutation, chromosome 15q partial deletion, and that the particular syndrome that a child has seems to depend on whether the mutation was inherited from the child's mother or father. This suggests that inherited aspects of development may depend on more than just the "conventional" genome. Angelman syndrome (AS) is neurological disorder in which severe learning difficulties are associated with a characteristic facial appearance and behavior. ... Prader-Willi syndrome is a genetic disorder in which seven genes (or some subset thereof) on chromosome 15 are missing or unexpressed (chromosome 15q partial deletion). ... 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. ...

See also

• Centromere
• Imprinting
• Maternal effect
• Paramutation
• Prion
• Weismann barrier

The centromere is a region of a eukaryotic chromosome where the kinetochore is assembled. ... Genomic imprinting is the phenomenon whereby a small subset of all the genes in our genome are expressed according to their parent of origin. ... A maternal effect, in genetics, is the phenomena where the genotype of a mother is expressed in the phenotype of its offspring. ... Paramutation, in genetics, is an interaction between two alleles of a single locus, resulting in a heritable change of one allele. ... This article has been identified as possibly containing errors. ... The Weismann barrier is the principle that hereditary information moves only from genes to body cells but never in reverse. ...

References

1. G.W. Grimes; K.J. Aufderheide; Cellular Aspects of Pattern Formation: the Problem of Assembly. Monographs in Developmental Biology, Vol. 22. Karger, Basel (1991)
2. E. Jablonka; M. Lachmann and M.J. Lamb; Evidence, mechanisms and models for the inheritance of acquired characteristics, J. Theoret. Biol. 158: 245-268 (1992)
3. K.D. Tremblay; J.R. Saam; R.S. Ingram; S.M. Tilghman and M.S. Bartolomei; A paternal-specific methylation imprint marks the alleles of the mouse H19 gene. Nature Genet. 9: 407-413 (1995)