Recombination and Mammalian Genome Evolution

Adam Eyre-Walker

Abstract

Several lines of evidence are presented which suggest that sequence G+C content and recombination frequency are related in mammals: (i) chromosome G+C content is positively correlated to chiasmata density; (ii) the non-pairing region of the Y chromosome has one of the lowest G+C contents of any chromosomal segment; (iii) a reduction in the rate of recombination at several loci is mirrored by a decrease in G+C content; and (iv) when compared with humans, mice have a lower variance in chiasmata density which is reflected in a lower variance in G+C content. The observed relation between recombination frequency and sequence G+C content provides an elegant explanation of why gene density is higher in G+C rich isochores than in other parts of the genome, and why long interspersed elements (LINES) are exclusive to G+C poor isochores. However, the cause of the relation is as yet unknown. Several possibilities are considered, including gene conversion.