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Encyclopedia > Gene conversion
The difference between gene conversion and chromosomal crossover. Blue are the two chromatids of one chromosome and red are the two chromatids of another one.
The difference between gene conversion and chromosomal crossover. Blue are the two chromatids of one chromosome and red are the two chromatids of another one.

Gene conversion is an event in DNA genetic recombination, which occurs during meiotic division. It is a process by which DNA sequence information is transferred from one DNA helix (which remains unchanged) to another DNA helix, whose sequence is altered. It is one of the ways a gene may be mutated. Gene conversion may lead to non-Mendelian inheritance and has often recorded in fungal crosses.[1] Thomas Hunt Morgans illustration of crossing over (1916) Homologous Recombination is the process by which two chromosomes, paired up during prophase I of meiosis, exchange some distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but... A chromatid forms one part of a chromosome after it has coalesced for the process of mitosis or meiosis. ... Genetic recombination is the process by which a strand of the genetic material (usually DNA; but can also be RNA) is broken and then joined to the end of a different DNA molecule. ... For the figure of speech, see meiosis (figure of speech). ... In genetics, non-Mendelian inheritance is the passing on of a trait in a form other than through chromosomal inheritance. ...

Contents

Mechanism

This conversion of one allele to the other is due to inappropriate base mismatch repair during recombination: if one of the four strands during meiosis pairs up with one of the four strands of a different chromosome, as can occur if there is sequence homology, repair can alter the sequence of one of the chromosomes, so that it is identically to the other. A scheme of a condensed (metaphase) chromosome. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ...


Gene conversion can result from the repair of damaged DNA as described by the Double Strand Break Repair Model. Here a break in both strands of DNA is repaired off of an intact homologous region of DNA. Resection (degradation) of the DNA strands near the break site leads to stretches of single stranded DNA that can invade the homologous DNA strand. The intact DNA is can then function as a template to copy the lost DNA. During this repair process a structure called a Double Holliday Structure is formed. Depending on how this structure is resolved (taken appart) either cross-over or gene conversion products result.


Effect

Normally, an organism that has inherited different copies of a gene from each of its parents is called heterozygous. This is generically represented as genotype: Aa (i.e. one copy of variant (allele) 'A', and one copy of allele 'a'). When a heterozygote creates gametes by meiosis, the alleles normally split, and end up in a 1:1 ratio in the resulting cells. However, in gene conversion, the ratio becomes other than the expected 1A:1a is observed, in which A and a are the two alleles. Such examples are 3A:1a, 1A:3a, 5A:3a or 3A:5a. In other words, there can for example be three times as many A alleles than a alleles expressed in the daughter cells, as is the case in 3A:1a. For the hard rock band, see Allele (band). ... For the figure of speech, see meiosis (figure of speech). ...


Importance of gene conversion in the cohesiveness of the gene pool

Gene conversion acts to homogenize the DNA sequences composing the gene pool of a species.[2] Every gene conversion event takes as its substrate two DNA sequences that are homologous but not identical, because of sequence mismatches and yields two identical DNA sequences. Gene conversion forms the cohesive force that links DNA sequences within different organisms of a species. Over time, gene conversion events yield a homogenous set of DNA sequences, both for allelic forms of a gene and for multi gene families. Interspersed repeats act to break up this linkage and catalyze the formation of novel gene during evolution. The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. ... For other uses, see Species (disambiguation). ... For the hard rock band, see Allele (band). ... A gene family is a set of genes defined by presumed homology, i. ... Interspersed repetitive DNA is found in all eukaryotic genomes. ...


References

  1. ^ Stacey, K. A. 1994. Recombination. In: Kendrew John, Lawrence Eleanor (eds.). The Encyclopedia of Molecular Biology. Oxford: Blackwell Science, 945–950.
  2. ^ Kull, Kalevi 2000. Organisms can be proud to have been their own designers. Cybernetics and Human Knowing 7(1): 45–55.[[1]]

External links

  • MeSH Gene+conversion
  • images: http://www.web-books.com/moBio/Free/Ch8D4.htm and http://www.web-books.com/moBio/Free/Ch8D2.htm
Molecular evolution is the process of the genetic material in populations of organisms changing over time. ... For other uses, see Natural selection (disambiguation). ... The term background selection refers to the reduction in genetic variation that occurs in the genomic area surrounding a gene that repeatedly mutates to a bad version. ... Sickle-shaped red blood cells Balancing selection refers to forms of natural selection which work to maintain genetic polymorphisms (or multiple alleles) within a population. ... In population genetics, directional selection (sometimes referred to as positive selection) occurs when natural selection favors a single allele and therefore allele frequency continuously shifts in one direction. ... Disruptive selection is a type of evolution that simultaneously favors individuals at both extremes of the distribution. ... It has been suggested that this article or section be merged with Stabilizing selection. ... A chart showing three types of selection Stabilizing selection, also referred to as purifying selection, is a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. ... A selective sweep is the reduction or elimination of variation among the nucleotides in neighbouring DNA of a mutation as the result of recent and strong natural selection. ... A number of different Markov models of DNA sequence evolution have been proposed. ... Models of nucleotide substitution are mathematical equations built to predict the probability (or proportion) of nucleotide change expected in a sequence. ... Allele frequency is a measure of the relative frequency of an allele on a genetic locus in a population. ... In genetics, the Ka/Ks ratio is the ratio of non-synonymous substitutions (Ka) to synonymous substitutions (Ks), which can be used as an indication of a protein-coding gene. ... Tajimas D is a statistical test created by and named after the Japanese researcher Fumio Tajima. ... Schematic of a region of a chromosome before and after a duplication event Gene duplication occurs when an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome leads to the duplication of a region of DNA containing a gene [1]. The significance of this process for... Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ... A synonymous substitution (also called a silent substitution) is the evolutionary substitution of one base for another in an exon of a gene coding for a protein, such that the amino acid sequence produced is not modified. ...

  Results from FactBites:
 
BioMed Central | Full text | Gene conversion homogenizes the CMT1A paralogous repeats (4091 words)
Gene conversion processes are similarly likely to play an important role in the evolution of other segmental duplications and may influence the rate of non-allelic homologous recombination between them.
Inverted paralogous repeats are responsible for the inversion of a portion of the factor VIII gene that causes hemophilia [7].
The first model assumes a random initiation of gene conversion along the sequence followed by branch migration that results in a geometric distribution of converted sequence, with a mean length of 353 bp [19], and is abbreviated as HI994.
W. Engels, recent paper abstracts (2975 words)
The distribution of conversion tract endpoints was indistinguishable from the distribution of crossover points among the non rearranged male recombinants.
The distribution of conversion tracts was found to be largely unaffected by changes in the length of sequence homology between the broken ends and the template, suggesting that only a short match is required.
The process is similar to gene conversion in its requirement for a homolog that is wild type at the insertion site, and in its reduced frequency when pairing between the homologs is inhibited.
  More results at FactBites »

 
 

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