Chromosome-wide linkage disequilibrium caused by an inversion polymorphism in the white-throated sparrow (Zonotrichia albicollis).
Chromosomal inversions have been of long-standing interest to geneticists because they are capable of suppressing recombination and facilitating the formation of adaptive gene complexes. An exceptional inversion polymorphism (ZAL2(m)) in the white-throated sparrow (Zonotrichia albicollis) is linked to variation in plumage, social behavior and mate choice, and is maintained in the population by negative assortative mating. The ZAL2(m) polymorphism is a complex inversion spanning > 100 Mb and has been proposed to be a strong suppressor of recombination, as well as a potential model for studying neo-sex chromosome evolution. To quantify and evaluate these features of the ZAL2(m) polymorphism, we generated sequence from 8 ZAL2(m) and 16 ZAL2 chromosomes at 58 loci inside and 4 loci outside the inversion. Inside the inversion we found that recombination was completely suppressed between ZAL2 and ZAL2(m), resulting in uniformly high levels of genetic differentiation (F(ST)=0.94), the formation of two distinct haplotype groups representing the alternate chromosome arrangements and extensive linkage disequilibrium spanning ~104 Mb within the inversion, whereas gene flow was not suppressed outside the inversion. Finally, although ZAL2(m) homozygotes are exceedingly rare in the population, occurring at a frequency of < 1%, we detected evidence of historical recombination between ZAL2(m) chromosomes inside the inversion, refuting its potential status as a non-recombining autosome.
Huynh
L Y
LY
Graduate Program in Population Biology, Ecology and Evolution, Emory University, Atlanta, GA, USA.
Maney
D L
DL
Thomas
J W
JW
D000818:Animals; D007446:Chromosome Inversion; D002875:Chromosomes / Q000235:genetics*; D015810:Linkage Disequilibrium; D008969:Molecular Sequence Data; D010802:Phylogeny; D011110:Polymorphism, Genetic; D011995:Recombination, Genetic; D046370:Sparrows / Q000145:classification / Q000235:genetics*