title: Effect of gene conversion on polymorphic patterns at major histocompatibility complex loci.
abstract: The pattern of polymorphisms at MHC loci was studied by computer simulations and by DNA sequence analyses, with special reference to synonymous and non-synonymous divergence among alleles. A model of overdominance plus short-term selection was simulated for a gene family with allelic and non-allelic gene conversion. It was found that the ratio of non-synonymous-to-synonymous divergence among alleles decreases as the non-allelic conversion becomes more frequent. On the other hand, the ratio of synonymous divergence at the antigen recognition site to that at non-coding region increases by non-allelic conversion. By comparing such a pattern with the observed values of mammalian genes, it is suggested that non-allelic conversion is less frequent in human genes than in genes of other mammals. A quantitative analysis on the patchwork pattern was attempted by using identity excess among nucleotide sites of a gene. Comparison of simulation results with DNA data analysis shows that the rate of allelic conversion is high.
mesh_terms: D000818:Animals; D001482:Base Composition; D005785:Gene Conversion / Q000276:immunology*; D006801:Humans; D008285:Major Histocompatibility Complex / Q000235:genetics* / Q000276:immunology*; D011110:Polymorphism, Genetic / Q000276:immunology*