Evolutionary rate of a gene affected by chromosomal position.
Genes evolve at different rates depending on the strength of selective pressure to maintain their function. Chromosomal position can also have an influence [1] [2]. The pseudoautosomal region (PAR) of mammalian sex chromosomes is a small region of sequence identity that is the site of an obligatory pairing and recombination event between the X and Y chromosomes during male meiosis [3] [4] [5] [6]. During female meiosis, X chromosomes can pair and recombine along their entire length. Recombination in the PAR is therefore approximately 10 times greater in male meiosis compared with female meiosis [4] [5] [6]. The gene Fxy (also known as MID1 [7]) spans the pseudoautosomal boundary (PAB) in the laboratory mouse (Mus musculus domesticus, C57BL/6) such that the 5' three exons of the gene are located on the X chromosome but the seven exons encoding the carboxy-terminal two-thirds of the protein are located within the PAR and are therefore present on both the X and Y chromosomes [8]. In humans [7] [9], the rat, and the wild mouse species Mus spretus, the gene is entirely X-unique. Here, we report that the rate of sequence divergence of the 3' end of the Fxy gene is much higher (estimated at 170-fold higher for synonymous sites) when pseudoautosomal (present on both the X and Y chromosomes) than when X-unique. Thus, chromosomal position can directly affect the rate of evolution of a gene. This finding also provides support for the suggestion that regions of the genome with a high recombination frequency, such as the PAR, may have an intrinsically elevated rate of sequence divergence.
Perry
J
J
Section of Gene Function and Regulation Chester Beatty Laboratories Institute of Cancer Research, 237 Fulham Road, London, SW3 6JB, UK.
Ashworth
A
A
D000818:Animals; D002874:Chromosome Mapping; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D005796:Genes; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL / Q000235:genetics*; D009115:Muridae / Q000235:genetics*; D010802:Phylogeny; D011506:Proteins / Q000235:genetics*; D051381:Rats / Q000235:genetics*; D012641:Selection, Genetic; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D044767:Ubiquitin-Protein Ligases; D014960:X Chromosome / Q000235:genetics*; D014998:Y Chromosome / Q000235:genetics*
D018076:DNA, Complementary; D011506:Proteins; C109037:Mid1 protein, mouse; D044767:Ubiquitin-Protein Ligases