UC Irvine

We have investigated nucleotide polymorphism at the β-esterase gene cluster including the Est-6 gene and ψEst-6 putative pseudogene in four samples of Drosophila melanogaster derived from natural populations of southern Africa (Zimbabwe), Europe (Spain), North America (USA: California), and South America (Venezuela). A complex haplotype structure is revealed in both Est-6 and ψEst-6. Total nucleotide diversity is twice in ψEst-6 as in Est-6; diversity is higher in the African sample than in the non-African ones. Strong linkage disequilibrium occurs within the β-esterase gene cluster in non-African samples, but not in the African one. Intragenic gene conversion events are detected within Est-6 and, to a much greater extent, within ψEst-6; intergenic gene conversion events are rare. Tests of neutrality with recombination are significant for the β-esterase gene cluster in the non-African samples but not significant in the African one. We suggest that the demographic history (bottleneck and admixture of genetically differentiated populations) is the major factor shaping the pattern of nucleotide polymorphism in the β-esterase gene cluster. However there are some 'footprints' of directional and balancing selection shaping specific distribution of nucleotide polymorphism within the cluster. Intergenic epistatic selection between Est-6 and ψEst-6 may play an important role in the evolution of the β-esterase gene cluster preserving the putative pseudogene from degenerative destruction and reflecting possible functional interaction between the functional gene and the putative pseudogene. Est-6 and ψEst-6 may represent an indivisible intergenic complex ('intergene') in which each single component (Est-6 or ψEst-6) cannot separately carry out the full functional role.