Abstract
We have investigated nucleotide polymorphism at the esterase 6 gene ( Est-6) gene, including the complete coding region (1686 bp), as well as the 5′-flanking (1183 bp) and 3′-flanking (193 bp) regions of the gene, in 30 strains of Drosophila melanogaster and in one strain of Drosophila simulans. The level of silent variation is similar in the coding and in the 3′-flanking region, but smaller in the 5′-flanking region. Strong linkage disequilibrium occurs within each region; and also, although less pronounced, between the 5′-flanking region and the rest of the gene, including the 3′-flanking region. We suggest that the pattern of nucleotide polymorphism of Est-6 may be shaped by: (1) directional and balancing selection acting on the promoter and the coding region; and (2) interactions between the two regions that involve variable degrees of hitchhiking. The patterns of linkage disequilibrium, as well as the statistics Z nS (Genetics 146 (1997)1197) and B and Q (Genet. Res. 74 (1999) 65), may be interpreted as there being multiple targets of selection within the gene. The previously reported Est-6 allozyme latitudinal clines may be accounted for by the interaction between selective processes in the promoter and coding regions.
Highlights
The esterase 6 (Est-6) gene is on the left arm of chromosome 3 of Drosophila melanogaster, 32.5 in the genetic map and at 68F7-F8 in the cytogenetic map
We investigate the 50-flanking, coding, and 30-flanking regions of the Est-6 gene (3062 bp total) in a random sample of 30 lines of D. melanogaster derived from a natural population of California
We suggest that the Est-6 nucleotide polymorphism is shaped by a combination of directional and balancing selection acting on the promoter and coding region polymorphisms, and by the interactions between the two regions due to different degrees of hitchhiking
Summary
The esterase 6 (Est-6) gene is on the left arm of chromosome 3 of Drosophila melanogaster, 32.5 in the genetic map and at 68F7-F8 in the cytogenetic map. The gene is duplicated (Collet et al, 1990) but there is evidence that the adjacently located duplicate, referred to as Est-P by Collet et al (1990) may be a pseudogene (cEst-6, Balakirev and Ayala, 1996). The EST-6 protein is transferred by D. melanogaster males to females in the seminal fluid during copulation and affects the female’s consequent behavior and mating proclivity (Richmond et al, 1990, and references therein). Two main allozymes (fast, F and slow, S) of EST-6 have been described, which manifest a differential response to the organophosphate inhibitor, which raises questions about the adaptive significance of the polymorphism. The main allozymes show large-scale repeatable latitudinal clines, with
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