Organization of nucleotide diversity within the third chromosomal inversions of Drosophila pseudoobscura. M. Kovacevic 1, M.P. Goetting-Minesky 1, J.G. Nelson 2, W.W. Anderson 2, S.W. Schaeffer 1. 1) Dept Biol, Pennsylvania State Univ, University Park, PA; 2) Dept Genetics, University of Georgia, Athens, GA.
Dobzhansky's (1948 Genetics 33: 588-602; 1950 Genetics 35: 288-302) work on the genetic basis of the third chromosomal inversion polymorphism in Drosophila pseudoobscura suggested that strong epistatic interactions existed among genes within and between inversions. This so called coadapted gene complex hypothesis predicts that the genetic contents of homosequential inversions collected from different populations will carry different gene combinations. We test this hypothesis with a nucleotide sequence analysis of five genes ( engrailed, exuperantia-1, vestigial, Amylase, and even-skipped) distributed across the third chromosome of D. pseudoobscura. Isofemale lines from four populations, Mt. St. Helena, CA; James Reserve, CA; Kaibab National Forest, AZ; and Davis Mountains, TX) were used to derive isochromosomal lines for third chromosomal inversions. A total of 400 to 500 bases were sequenced for each genetic marker in 5 to 10 strains carrying the ST, CH, and AR chromosomal inversions from each population. We tested each genetic locus for significant genetic differentiation within inversion type among populations with the Hudson, Boos, and Kaplan test of geographic subdivision (MBE 9: 138-151). Phylogenetic analysis of the Amylase and vestigial genes shows strong concordance with the cytological phylogeny, while the phylogenies of even-skipped, exuperantia, and engrailed are not completely concordant with the inversion phylogeny. The analysis of the genetic differentiation of genes within inversions between populations will be discussed with respect to the coadapted gene complex hypothesis.