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 eukaryotes
recombination commonly occurs during meiosis
as chromosomal crossover
between paired chromosomes. This process leads to offspring having different combinations of genes from their parents and can produce new chimeric alleles
. In evolutionary biology this shuffling of genes is thought to have many advantages, including that of allowing sexually reproducing organisms to avoid Muller's ratchet
In molecular biology "recombination" can also refer to artificial and deliberate recombination of disparate pieces of DNA, often from different organisms, creating what is called recombinant DNA.
Enzymes called recombinases catalyze natural recombination reactions. RecA, the recombinase found in E. coli, is responsible for the repair of DNA double strand breaks (DSBs). In yeast and other eukaryotic organisms there are two recombinases required for repairing DSBs. The RAD51 protein is required for mitotic and meiotic recombination and the DMC1 protein is specific to meiotic recombination.
Chromosomal crossover refers to recombination between the paired chromosomes inherited from each of one's parents, generally occurring during meiosis. During prophase I the four available chromatids are in tight formation with one another. While in this formation, homologous sites on two chromatids can mesh with one another, and may exchange genetic information.
Because recombination can occur with small probability at any location along chromosome, the frequency of recombination between two locations depends on their distance. Therefore, for genes sufficiently distant on the same chromosome the amount of crossover is high enough to destroy the correlation between alleles.
In gene conversion, a section of genetic material is copied from one chromosome to another, but leaves the donating chromosome unchanged.
Recombination can occur between DNA sequences that contain no sequence homology. This is referred to as Nonhomologous recombination or nonhomologous end joining.
- Alberts, B. et al., Molecular Biology of the Cell, 3rd Edition. Garland Publishing, 1994.