title: Molecular evolution of the Sex-Ratio inversion complex in Drosophila pseudoobscura: analysis of the Esterase-5 gene region.
abstract: The Sex-Ratio chromosome in Drosophila pseudoobscura is subject to meiotic drive. It is associated with a series of three nonoverlapping paracentric inversions on the right arm of the X chromosome. The esterase-5 gene region has been localized to section 23 within the subbasal inversion of the Sex-Ratio inversion complex, making esterase-5 a convenient locus for molecular evolutionary analyses of the Sex-Ratio inversion complex and the associated drive system. A 504-bp fragment of noncoding, intergenic DNA from the esterase-5 gene region was amplified and sequenced from 14 Sex-Ratio and 14 Standard X chromosomes of D. pseudoobscura, and from 9 X chromosomes of its two sibling species, Drosophila persimilis and Drosophila miranda. There is extensive sequence differentiation between the Sex-Ratio and Standard chromosomal types. The common Standard chromosome is highly polymorphic, while, as expected from either the neutral mutation theory or the selective sweep hypothesis, the rarer Sex-Ratio chromosome has much less within-chromosome nucleotide polymorphism. We estimate that the Standard and Sex-Ratio chromosomes in D. pseudoobscura diverged between 700,000 and 1.3 Mya, or at least 2 million generations ago. The clustering of D. pseudoobscura Sex-Ratio chromosomes in a neighbor-joining phylogeny indicates a fairly old, monophyletic origin in this species. It appears from these data that Sex-Ratio genes were present prior to the divergence of D. pseudoobscura and D. persimilis and that both the Standard and Sex-Ratio chromosomes of D. persimilis were derived from the Standard chromosome of D. pseudoobscura after the inversion events that isolated the D. pseudoobscura Sex-Ratio chromosome.
authors.affiliation: Department of Genetics, University of Georgia, Athens 30602-1732, USA.
authors.forename: C S
authors.initials: CS
authors.lastname: Babcock
authors.forename: W W
authors.initials: WW
authors.lastname: Anderson
mesh_terms: D000818:Animals; D001483:Base Sequence; D007446:Chromosome Inversion; D004330:Drosophila / Q000145:classification / Q000235:genetics*; D004950:Esterases / Q000235:genetics*; D019143:Evolution, Molecular; D005260:Female; D005819:Genetic Markers; D008297:Male; D008540:Meiosis; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D012744:Sex Ratio; D013045:Species Specificity; D014960:X Chromosome / Q000648:ultrastructure*
chemical_list: D005819:Genetic Markers; D004950:Esterases