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. A chromatid is one of two identical copies of DNA making up a replicated Chromosome, which are joined at their Centromeres for the process of Cell division

Gene conversion is an event in DNA genetic recombination, which occurs during meiotic division. Genetic recombination is the process by which a strand of genetic material (usually DNA; but can also be RNA) is broken and then joined to a different DNA molecule In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half 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 been recorded in fungal crosses. Non-Mendelian inheritance is a general term that refers to any pattern of inheritance in which traits do not segregate in accordance with Mendel’s laws ^[1]

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, mismatch repair can alter the sequence of one of the chromosomes, so that it is identical to the other. A chromosome is an organized structure of DNA and Protein that is found in cells. In Evolutionary biology, homology has come to mean any similarity between characters 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 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 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 apart) 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'). An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms When a heterozygote creates gametes by meiosis, the alleles normally split, and end up in a 1:1 ratio in the resulting cells. In Biology or life science meiosis (pronounced my-oh-sis is a process of reductional division in which the number of chromosomes per cell is cut in half 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.

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. In Population genetics, a gene pool is the complete set of unique Alleles in a Species or Population. ^[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. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Over time, gene conversion events yield a homogenous set of DNA sequences, both for allelic forms of a gene and for multi gene families. An allele (ˈæliːl (UK /əˈliːl/ (US (from the Greek αλληλος allelos, meaning each other) is one member of a pair or series of different forms A gene family is a set of Genes with a known homology. They are generally biochemically similar Interspersed repeats act to break up this linkage and catalyze the formation of novel gene during evolution. 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