MoBio Homologous Recombination Chapter 8

Homologous recombination occurs between two homologous DNA molecules. It is also called DNA crossover. During meiosis, two homologous pairs of sister chromatids align side by side. The DNA crossover is very likely to occur. It could be as often as several times per meiosis.

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Figure 8-D-1. DNA crossover. (a) Two homologous pairs of sister chromatids align side by side. (b) The two homologs are connected at a certain point called chiasma. (c) The two homologs exchange the DNA segment from the chiasma to the end of chromosomes.

The mechanism of DNA crossover was first explained by Robin Holliday in 1964 (More Info).

Due to significant sequence homology, the repetitive sequence region of a chromatid may not line up exactly with its corresponding region in a homologous chromatid or identical sister chromatid. This may result in unequal crossover, which is thought to be the major mechanism underlying VNTR (variable number of tandem repeats).

DNA crossover is not the same as gene conversion.