title: Sequence differentiation associated with an inversion on the neo-X chromosome of Drosophila americana.
abstract: Sex chromosomes originate from pairs of autosomes that acquire controlling genes in the sex-determining cascade. Universal mechanisms apparently influence the evolution of sex chromosomes, because this chromosomal pair is characteristically heteromorphic in a broad range of organisms. To examine the pattern of initial differentiation between sex chromosomes, sequence analyses were performed on a pair of newly formed sex chromosomes in Drosophila americana. This species has neo-sex chromosomes as a result of a centromeric fusion between the X chromosome and an autosome. Sequences were analyzed from the Alcohol dehydrogenase (Adh), big brain (bib), and timeless (tim) gene regions, which represent separate positions along this pair of neo-sex chromosomes. In the northwestern range of the species, the bib and Adh regions exhibit significant sequence differentiation for neo-X chromosomes relative to neo-Y chromosomes from the same geographic region and other chromosomal populations of D. americana. Furthermore, a nucleotide site defining a common haplotype in bib is shown to be associated with a paracentric inversion [In(4)ab] on the neo-X chromosome, and this inversion suppresses recombination between neo-X and neo-Y chromosomes. These observations are consistent with the inversion acting as a recombination modifier that suppresses exchange between these neo-sex chromosomes, as predicted by models of sex chromosome evolution.
authors.affiliation: Department of Biology, University of Texas, Arlington, Texas 76019, USA. bryant-mcallister@uiowa.edu
authors.forename: Bryant F
authors.initials: BF
authors.lastname: McAllister
mesh_terms: D000818:Animals; D007446:Chromosome Inversion; D004330:Drosophila / Q000235:genetics*; D019143:Evolution, Molecular; D005260:Female; D007621:Karyotyping; D008297:Male; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D014960:X Chromosome