Reduced variation on the chicken Z chromosome.
Understanding the population genetic factors that shape genome variability is pivotal to the design and interpretation of studies using large-scale polymorphism data. We analyzed patterns of polymorphism and divergence at Z-linked and autosomal loci in the domestic chicken (Gallus gallus) to study the influence of mutation, effective population size, selection, and demography on levels of genetic diversity. A total of 14 autosomal introns (8316 bp) and 13 Z-linked introns (6856 bp) were sequenced in 50 chicken chromosomes from 10 highly divergent breeds. Genetic variation was significantly lower at Z-linked than at autosomal loci, with one segregating site every 39 bp at autosomal loci (theta(W) = 5.8 +/- 0.8 x 10(-3)) and one every 156 bp on the Z chromosome (theta(W) = 1.4 +/- 0.4 x 10(-3)). This difference may in part be due to a low male effective population size arising from skewed reproductive success among males, evident both in the wild ancestor-the red jungle fowl-and in poultry breeding. However, this effect cannot entirely explain the observed three- to fourfold reduction in Z chromosome diversity. Selection, in particular selective sweeps, may therefore have had an impact on reducing variation on the Z chromosome, a hypothesis supported by the observation of heterogeneity in diversity levels among loci on the Z chromosome and the lower recombination rate on Z than on autosomes. Selection on sex-linked genes may be particularly important in organisms with female heterogamety since the heritability of sex-linked sexually antagonistic alleles advantageous to males is improved when fathers pass a Z chromosome to their sons.
Sundström
Hannah
H
Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, SE-752 36 Uppsala, Sweden.
Webster
Matthew T
MT
Ellegren
Hans
H
D000483:Alleles; D000818:Animals; D002645:Chickens / Q000235:genetics*; D004247:DNA / Q000235:genetics; D005260:Female; D014644:Genetic Variation; D005828:Genetics, Population; D006239:Haplotypes; D007438:Introns; D008297:Male; D015233:Models, Statistical; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes
D004247:DNA