Non-Mendelian inheritance

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Mirabilis jalapa Gul-Abas-4-O'clock plant.JPG
Mirabilis jalapa
Carl Correns Carl Correns.jpg
Carl Correns

Non-Mendelian inheritance is any pattern in which traits do not segregate in accordance with Mendel's laws. These laws describe the inheritance of traits linked to single genes on chromosomes in the nucleus. In Mendelian inheritance, each parent contributes one of two possible alleles for a trait. If the genotypes of both parents in a genetic cross are known, Mendel's laws can be used to determine the distribution of phenotypes expected for the population of offspring. There are several situations in which the proportions of phenotypes observed in the progeny do not match the predicted values.

Contents

Certain inherited diseases and their presentation display non-Mendelian patterns, complicating making predictions from family history. [1]

Types

Incomplete dominance, codominance, multiple alleles, and polygenic traits follow Mendel's laws, display Mendelian inheritance, and are explained as extensions of Mendel's laws. [2]

Incomplete dominance

Incomplete dominance - Antirrhinum majus.png

In cases of intermediate inheritance due to incomplete dominance, the principle of dominance discovered by Mendel does not apply. Nevertheless, the principle of uniformity works, as all offspring in the F1-generation have the same genotype and same phenotype. Mendel's principle of segregation of genes applies too, as in the F2-generation homozygous individuals with the phenotypes of the P-generation[ clarification needed ] appear. Intermediate inheritance was first examined by Carl Correns in flower colour of Mirabilis jalapa . [3] Antirrhinum majus also shows intermediate inheritance of the pigmentation of the blossoms. [4]

Co-dominance

Co-dominant expression of genes for plumage colours. Pavlovian black-white chicken rooster 1.jpg
Co-dominant expression of genes for plumage colours.

In cases of co-dominance, the genetic traits of both different alleles of the same gene-locus are clearly expressed in the phenotype. For example, in certain varieties of chicken, the allele for black feathers is co-dominant with the allele for white feathers. Heterozygous chickens have a colour described as "erminette", speckled with black and white feathers appearing separately. Many human genes, including one for a protein that controls cholesterol levels in the blood, show co-dominance too. People with the heterozygous form of this gene produce two different forms of the protein, each with a different effect on cholesterol levels.[ citation needed ]

Genetic linkage

When genes are located on the same chromosome and no crossing over took place before the segregation of the chromosomes into the gametes, the genetic traits will be inherited in connection, because of the genetic linkage. These cases constitute an exception to the Mendelian rule of independent assortment.[ citation needed ]

Multiple alleles

In Mendelian inheritance, genes have only two alleles, such as a and A. Mendel consciously chose pairs of genetic traits, represented by two alleles for his inheritance experiments. In nature, such genes often exist in several different forms and are therefore said to have multiple alleles. An individual usually has only two copies of each gene, but many different alleles are often found within a population. A rabbit's coat color is determined by a single gene that has at least four different alleles. They display a pattern of a dominance-hierarchy that can produce four coat colors. In the genes for the dog coat colours there are four alleles on the Agouti-locus. The allele "aw" is dominant over the alleles "at" and "a" but recessive under "Ay".[ citation needed ]

Many other genes have multiple alleles, including the human genes for ABO blood type.[ citation needed ]

Epistasis

In the genepool of cats (Felis catus) there is a recessive allele for orange coat on the X-Chromosome. In a male the Y-Chromosome cannot compensate this, so a tomcat with that allele is born orange. This allele is epistatic over some other coat color genes. Cat (30072497623).jpg
In the genepool of cats ( Felis catus ) there is a recessive allele for orange coat on the X-Chromosome. In a male the Y-Chromosome cannot compensate this, so a tomcat with that allele is born orange. This allele is epistatic over some other coat color genes.
A heterozygous cat with kittens from an orange tomcat: 50 % are orange, 50 % can produce eumelanin. Here the segregation of her two alleles, one dominant for the ability to produce eumelanin, one recessive for orange, was crucial for the colour of the kittens. With the young males it is decisive which of the two X-Chromosomes they received from the mother, because the Y-Chromosome does not contain a corresponding allele from the father. In the young females it is also decisive which X-Chromosome they got from the mother, because they each have an allele for orange from the father and only homozygotes become orange. Charline the cat and her kittens.jpg
A heterozygous cat with kittens from an orange tomcat: 50 % are orange, 50 % can produce eumelanin. Here the segregation of her two alleles, one dominant for the ability to produce eumelanin, one recessive for orange, was crucial for the colour of the kittens. With the young males it is decisive which of the two X-Chromosomes they received from the mother, because the Y-Chromosome does not contain a corresponding allele from the father. In the young females it is also decisive which X-Chromosome they got from the mother, because they each have an allele for orange from the father and only homozygotes become orange.

If one or more genes cannot be expressed because of another genetic factor hindering their expression, this epistasis can make it impossible even for dominant alleles on certain other gene-loci to have an effect on the phenotype. An example in dog coat genetics is the homozygosity with the allele "e e" on the Extension-locus making it impossible to produce any other pigment than pheomelanin. Although the allele "e" is a recessive allele on the extension-locus itself, the presence of two copies leverages the dominance of other coat colour genes. Domestic cats have a gene with a similar effect on the X-chromosome.[ citation needed ]

Sex-linked inheritance

Genetic traits located on gonosomes sometimes show specific non-Mendelian inheritance patterns. Individuals can develop a recessive trait in the phenotype dependent on their sex—for example, colour blindness and haemophilia (see gonosomal inheritances). [7] [8] As many of the alleles are dominant or recessive, a true understanding of the principles of Mendelian inheritance is an important requirement to also understand the more complicated inheritance patterns of sex-linked inheritances.[ citation needed ]

Extranuclear inheritance

Example of a pedigree for a genetic trait inherited by mitochondrial DNA in animals and humans. Offspring of the males with the trait don't inherit the trait. Offspring of the females with the trait always inherit the trait (independently from their own sex). Maternal Inheritance - mitochondrial DNA.png
Example of a pedigree for a genetic trait inherited by mitochondrial DNA in animals and humans. Offspring of the males with the trait don't inherit the trait. Offspring of the females with the trait always inherit the trait (independently from their own sex).

Extranuclear inheritance (also known as cytoplasmic inheritance) is a form of non-Mendelian inheritance also first discovered by Carl Correns in 1908. [9] While working with Mirabilis jalapa, Correns observed that leaf colour was dependent only on the genotype of the maternal parent. Based on these data, he determined that the trait was transmitted through a character present in the cytoplasm of the ovule. Later research by Ruth Sager and others identified DNA present in chloroplasts as being responsible for the unusual inheritance pattern observed. Work on the poky strain of the mould Neurospora crassa begun by Mary and Hershel Mitchell [10] ultimately led to the discovery of genetic material in the mitochondria, the mitochondrial DNA.[ citation needed ]

According to the endosymbiont theory, mitochondria and chloroplasts were once free-living organisms that were each taken up by a eukaryotic cell. [11] Over time, mitochondria and chloroplasts formed a symbiotic relationship with their eukaryotic hosts. Although the transfer of a number of genes from these organelles to the nucleus prevents them from living independently, each still possesses genetic material in the form of double stranded DNA.[ citation needed ]

It is the transmission of this organellar DNA that is responsible for the phenomenon of extranuclear inheritance. Both chloroplasts and mitochondria are present in the cytoplasm of maternal gametes only. Paternal gametes (sperm for example) do not have cytoplasmic mitochondria[ citation needed ]. Thus, the phenotype of traits linked to genes found in either chloroplasts or mitochondria are determined exclusively by the maternal parent.

In humans, mitochondrial diseases are a class of diseases, many of which affect the muscles and the eye.[ citation needed ]

Polygenic traits

Many traits are produced by the interaction of several genes. Traits controlled by two or more genes are said to be polygenic traits. Polygenic means "many genes" are necessary for the organism to develop the trait. For example, at least three genes are involved in making the reddish-brown pigment in the eyes of fruit flies. Polygenic traits often show a wide range of phenotypes. The broad variety of skin colour in humans comes about partly because at least four different genes probably control this trait.[ citation needed ]

Non-random segregation

Non-random segregation of chromosomes is a deviation from the usual distribution of chromosomes during meiosis and in some cases of mitosis.

Gene conversion

Gene conversion can be one of the major forms of non-Mendelian inheritance. Gene conversion arises during DNA repair via DNA recombination, by which a piece of DNA sequence information is transferred from one DNA helix (which remains unchanged) to another DNA helix, whose sequence is altered. This may occur as a mismatch repair between the strands of DNA which are derived from different parents. Thus the mismatch repair can convert one allele into the other. This phenomenon can be detected through the offspring non-Mendelian ratios, and is frequently observed, e.g., in fungal crosses. [12]

Infectious heredity

Another form of non-Mendelian inheritance is known as infectious heredity. Infectious particles such as viruses may infect host cells and continue to reside in the cytoplasm of these cells. If the presence of these particles results in an altered phenotype, then this phenotype may be subsequently transmitted to progeny. [13] Because this phenotype is dependent only on the presence of the invader in the host cell's cytoplasm, inheritance will be determined only by the infected status of the maternal parent. This will result in a uniparental transmission of the trait, just as in extranuclear inheritance.[ citation needed ]

One of the most well-studied examples of infectious heredity is the killer phenomenon exhibited in yeast. Two double-stranded RNA viruses, designated L and M, are responsible for this phenotype. [14] The L virus codes for the capsid proteins of both viruses, as well as an RNA polymerase. Thus the M virus can only infect cells already harbouring L virus particles. The M viral RNA encodes a toxin that is secreted from the host cell. It kills susceptible cells growing in close proximity to the host. The M viral RNA also renders the host cell immune to the lethal effects of the toxin. For a cell to be susceptible it must therefore be either uninfected or harbour only the L virus.[ citation needed ]

The L and M viruses are not capable of exiting their host cell through conventional means. They can only transfer from cell to cell when their host undergoes mating. All progeny of a mating involving a doubly infected yeast cell will also be infected with the L and M viruses. Therefore, the killer phenotype will be passed down to all progeny.[ citation needed ]

Heritable traits that result from infection with foreign particles have also been identified in Drosophila . Wild-type flies normally fully recover after being anesthetized with carbon dioxide. Certain lines of flies have been identified that die off after exposure to the compound. This carbon dioxide sensitivity is passed down from mothers to their progeny. This sensitivity is due to infection with σ (Sigma) virus, a rhabdovirus only capable of infecting Drosophila. [15]

Although this process is usually associated with viruses, recent research has shown that the Wolbachia bacterium is also capable of inserting its genome into that of its host. [16] [17]

Genomic imprinting

Genomic imprinting represents yet another example of non-Mendelian inheritance. Just as in conventional inheritance, genes for a given trait are passed down to progeny from both parents. However, these genes are epigenetically marked before transmission, altering their levels of expression. These imprints are created before gamete formation and are erased during the creation of germ line cells. Therefore, a new pattern of imprinting can be made with each generation.[ citation needed ]

Genes are imprinted differently depending on the parental origin of the chromosome that contains them. In mice, the insulin-like growth factor 2 gene undergoes imprinting. The protein encoded by this gene helps to regulate body size. Mice that possess two functional copies of this gene are larger than those with two mutant copies. The size of mice that are heterozygous at this locus depends on the parent from which the wild-type allele came. If the functional allele originated from the mother, the offspring will exhibit dwarfism, whereas a paternal allele will generate a normal-sized mouse. This is because the maternal Igf2 gene is imprinted. Imprinting results in the inactivation of the Igf2 gene on the chromosome passed down by the mother. [18]

Imprints are formed due to the differential methylation of paternal and maternal alleles. This results in differing expression between alleles from the two parents. Sites with significant methylation are associated with low levels of gene expression. Higher gene expression is found at unmethylated sites. [19] In this mode of inheritance, phenotype is determined not only by the specific allele transmitted to the offspring, but also by the sex of the parent that transmitted it.

Mosaicism

Individuals who possess cells with genetic differences from the other cells in their body are termed mosaics. These differences can result from mutations that occur in different tissues and at different periods of development. If a mutation happens in the non-gamete forming tissues, it is characterized as somatic. Germline mutations occur in the egg or sperm cells and can be passed on to offspring. [20] Mutations that occur early on in development will affect a greater number of cells and can result in an individual that can be identified as a mosaic strictly based on phenotype.

Mosaicism also results from a phenomenon known as X-inactivation. All female mammals have two X chromosomes. To prevent lethal gene dosage problems, one of these chromosomes is inactivated following fertilization. This process occurs randomly for all of the cells in the organism's body. Because a given female's two X chromosomes will almost certainly differ in their specific pattern of alleles, this will result in differing cell phenotypes depending on which chromosome is silenced. Calico cats, which are almost all female, [21] demonstrate one of the most commonly observed manifestations of this process. [22]

Trinucleotide repeat disorders

Trinucleotide repeat disorders also follow a non-Mendelian pattern of inheritance. These diseases are all caused by the expansion of microsatellite tandem repeats consisting of a stretch of three nucleotides. [23] Typically in individuals, the number of repeated units is relatively low. With each successive generation, there is a chance that the number of repeats will expand. As this occurs, progeny can progress to premutation and ultimately affected status. Individuals with a number of repeats that falls in the premutation range have a good chance of having affected children. Those who progress to affected status will exhibit symptoms of their particular disease. Prominent trinucleotide repeat disorders include Fragile X syndrome and Huntington's disease. In the case of Fragile X syndrome it is thought that the symptoms result from the increased methylation and accompanying reduced expression of the fragile X intellectual disability gene in individuals with a sufficient number of repeats. [24]

See also

Related Research Articles

An allele, or allelomorph, is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule.

<span class="mw-page-title-main">Genetics</span> Science of genes, heredity, and variation in living organisms

Genetics is the study of genes, genetic variation, and heredity in organisms. It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar working in the 19th century in Brno, was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring over time. He observed that organisms inherit traits by way of discrete "units of inheritance". This term, still used today, is a somewhat ambiguous definition of what is referred to as a gene.

The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a specific gene depends on the number of copies of each chromosome found in that species, also referred to as ploidy. In diploid species like humans, two full sets of chromosomes are present, meaning each individual has two alleles for any given gene. If both alleles are the same, the genotype is referred to as homozygous. If the alleles are different, the genotype is referred to as heterozygous.

<span class="mw-page-title-main">Heredity</span> Passing of traits to offspring from the species parents or ancestor

Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents. Through heredity, variations between individuals can accumulate and cause species to evolve by natural selection. The study of heredity in biology is genetics.

<span class="mw-page-title-main">Mendelian inheritance</span> Type of biological inheritance

Mendelian inheritance is a type of biological inheritance following the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and later popularized by William Bateson. These principles were initially controversial. When Mendel's theories were integrated with the Boveri–Sutton chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics. Ronald Fisher combined these ideas with the theory of natural selection in his 1930 book The Genetical Theory of Natural Selection, putting evolution onto a mathematical footing and forming the basis for population genetics within the modern evolutionary synthesis.

<span class="mw-page-title-main">Dominance (genetics)</span> One gene variant masking the effect of another in the other copy of the gene

In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and the second is called recessive. This state of having two different variants of the same gene on each chromosome is originally caused by a mutation in one of the genes, either new or inherited. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes (autosomes) and their associated traits, while those on sex chromosomes (allosomes) are termed X-linked dominant, X-linked recessive or Y-linked; these have an inheritance and presentation pattern that depends on the sex of both the parent and the child. Since there is only one copy of the Y chromosome, Y-linked traits cannot be dominant or recessive. Additionally, there are other forms of dominance, such as incomplete dominance, in which a gene variant has a partial effect compared to when it is present on both chromosomes, and co-dominance, in which different variants on each chromosome both show their associated traits.

Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart. In other words, the nearer two genes are on a chromosome, the lower the chance of recombination between them, and the more likely they are to be inherited together. Markers on different chromosomes are perfectly unlinked, although the penetrance of potentially deleterious alleles may be influenced by the presence of other alleles, and these other alleles may be located on other chromosomes than that on which a particular potentially deleterious allele is located.

A quantitative trait locus (QTL) is a locus that correlates with variation of a quantitative trait in the phenotype of a population of organisms. QTLs are mapped by identifying which molecular markers correlate with an observed trait. This is often an early step in identifying the actual genes that cause the trait variation.

Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.

Genetics, a discipline of biology, is the science of heredity and variation in living organisms.

Intragenomic conflict refers to the evolutionary phenomenon where genes have phenotypic effects that promote their own transmission in detriment of the transmission of other genes that reside in the same genome. The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects cause their transmission to new organisms, and most genes achieve this by cooperating with other genes in the same genome to build an organism capable of reproducing and/or helping kin to reproduce. The assumption of the prevalence of intragenomic cooperation underlies the organism-centered concept of inclusive fitness. However, conflict among genes in the same genome may arise both in events related to reproduction and altruism.

<span class="mw-page-title-main">Test cross</span> Concept in classical genetics

Under the law of dominance in genetics, an individual expressing a dominant phenotype could contain either two copies of the dominant allele or one copy of each dominant and recessive allele. By performing a test cross, one can determine whether the individual is heterozygous or homozygous dominant.

<span class="mw-page-title-main">Gene</span> Sequence of DNA or RNA that codes for an RNA or protein product

In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and non-coding genes.

The following outline is provided as an overview of and topical guide to genetics:

Uniparental inheritance is a non-Mendelian form of inheritance that consists of the transmission of genotypes from one parental type to all progeny. That is, all the genes in offspring will originate from only the mother or only the father. This phenomenon is most commonly observed in eukaryotic organelles such as mitochondria and chloroplasts. This is because such organelles contain their own DNA and are capable of independent mitotic replication that does not endure crossing over with the DNA from another parental type. Although uniparental inheritance is the most common form of inheritance in organelles, there is increased evidence of diversity. Some studies found doubly uniparental inheritance (DUI) and biparental transmission to exist in cells. Evidence suggests that even when there is biparental inheritance, crossing-over doesn't always occur. Furthermore, there is evidence that the form of organelle inheritance varied frequently over time. Uniparental inheritance can be divided into multiple subtypes based on the pathway of inheritance.

Classical genetics is the branch of genetics based solely on visible results of reproductive acts. It is the oldest discipline in the field of genetics, going back to the experiments on Mendelian inheritance by Gregor Mendel who made it possible to identify the basic mechanisms of heredity. Subsequently, these mechanisms have been studied and explained at the molecular level.

Oligogenic inheritance describes a trait that is influenced by a few genes. Oligogenic inheritance represents an intermediate between monogenic inheritance in which a trait is determined by a single causative gene, and polygenic inheritance, in which a trait is influenced by many genes and often environmental factors.

This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. It has been designed as a companion to Glossary of cellular and molecular biology, which contains many overlapping and related terms; other related glossaries include Glossary of biology and Glossary of ecology.

<span class="mw-page-title-main">Complex traits</span>

Complex traits are phenotypes that are controlled by two or more genes and do not follow Mendel's Law of Dominance. They may have a range of expression which is typically continuous. Both environmental and genetic factors often impact the variation in expression. Human height is a continuous trait meaning that there is a wide range of heights. There are an estimated 50 genes that affect the height of a human. Environmental factors, like nutrition, also play a role in a human's height. Other examples of complex traits include: crop yield, plant color, and many diseases including diabetes and Parkinson's disease. One major goal of genetic research today is to better understand the molecular mechanisms through which genetic variants act to influence complex traits. Complex traits are also known as polygenic traits and multigenic traits.

Biparental inheritance is a type of biological inheritance where the progeny inherits a maternal and a paternal allele for one gene. It is one of the criteria for Mendelian inheritance. Sexual reproduction, where offspring result from the fusion of gametes from two parents, is the most common form of biparental inheritance. While less common, cases of biparental inheritance in extranuclear genes have been documented, such as biparental inheritance of mitochondrial DNA, or chloroplast DNA in plants. Biparental inheritance of nuclear DNA by way of sexual reproduction can allow for new combinations of alleles from each contributing parent. The production of gametes through meiosis can sometimes include recombination, or crossing-over, which is a possibility for novel combinations of alleles.

References

  1. ↑ Van Heyningen V, Yeyati PL (2004). "Mechanisms of non-Mendelian inheritance in genetic disease". Hum. Mol. Genet. 13 Spec No 2: R225–33. doi: 10.1093/hmg/ddh254 . PMID   15358729.
  2. ↑ Hartwell, L. (2000). *Genetics: From Genes to Genomes*. United Kingdom: McGraw-Hill. Page 39.
  3. ↑ Biology University of Hamburg: Mendelian Genetics
  4. ↑ Neil A. Campbell, Jane B. Reece: Biologie. Spektrum-Verlag Heidelberg-Berlin 2003, ISBN   3-8274-1352-4, page 302.
  5. ↑ Schmidt-Küntzel, Nelson G. David et al.: A domestic cat X chromosome linkage map and the sex-linked orange locus: mapping of orange, multiple origins and epistasis over nonagouti.
  6. ↑ Le gène Orange chez le chat : génotype et phénotype
  7. ↑ Joseph Schacherer: Beyond the simplicity of Mendelian inheritance Science Direct 2016
  8. ↑ Khan Academy: Variations on Mendel's laws (overview)
  9. ↑ Klug, William S.; Michael R. Cummings; Charlotte A. Spencer (2006). Concepts of Genetics . Upper Saddle River, NJ: Pearson Education Inc. p.  215. ISBN   9780131918337.
  10. ↑ Mitchell MB, Mitchell HK (1952). "A case of "maternal" inheritance in Neurospora crassa". Proc. Natl. Acad. Sci. U.S.A. 38 (5): 442–9. Bibcode:1952PNAS...38..442M. doi: 10.1073/pnas.38.5.442 . PMC   1063583 . PMID   16589122.
  11. ↑ Embley, T. Martin; William Martin (March 2006). "Eukaryotic evolution, changes and challenges". Nature. 440 (7084): 623–630. Bibcode:2006Natur.440..623E. doi:10.1038/nature04546. PMID   16572163. S2CID   4396543.
  12. ↑ Stacey K. A. (1994). Recombination. In: Kendrew John, Lawrence Eleanor (eds.
  13. ↑ Klug, William S.; Michael R. Cummings; Charlotte A. Spencer (2006). Concepts of Genetics . Upper Saddle River, NJ: Pearson Education Inc. p.  223. ISBN   9780131918337.
  14. ↑ Russell, Peter J. (2006). iGenetics: A Mendelian Approach. San Francisco: Pearson Education, Inc. pp. 649–650.
  15. ↑ Teninges, Danielle; Francoise Bras-Herreng (July 1987). "Rhabdovirus Sigma, the Hereditary CO2 Sensitivity Agent of Drosophila:Nucleotide Sequence of a cDNA Clone Encoding the Glycoprotein". Journal of General Virology. 68 (10): 2625–2638. doi: 10.1099/0022-1317-68-10-2625 . PMID   2822842.
  16. ↑ "University of Rochester Press Releases" . Retrieved 2007-10-16.
  17. ↑ Dunning Hotopp JC, Clark ME, Oliveira DC, et al. (2007). "Widespread lateral gene transfer from intracellular bacteria to multicellular eukaryotes" (PDF). Science. 317 (5845): 1753–6. Bibcode:2007Sci...317.1753H. CiteSeerX   10.1.1.395.1320 . doi:10.1126/science.1142490. PMID   17761848. S2CID   10787254.
  18. ↑ Bell, A.C.; G. Felsenfeld (2000). "Methylation of a CTCF-dependent boundar control imprinted expression of the Igf2 gene". Nature. 405 (6785): 482–485. Bibcode:2000Natur.405..482B. doi:10.1038/35013100. PMID   10839546. S2CID   4387329.
  19. ↑ Lewin, Benjamin (2004). Genes VIII. Upper Saddle River, NJ: Pearson Education Inc. pp. 680–684.
  20. ↑ "Lesson 3: Mosaicism" . Retrieved 2007-10-16.
  21. ↑ "Genetics of Calico Color".
  22. ↑ "Genetic Mosaicism" . Retrieved 2007-10-28.
  23. ↑ "Lesson 1: Triplet Repeat Expansion" . Retrieved 2007-10-16.
  24. ↑ "FMR1-Related Disorders" . Retrieved 2007-10-29.
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