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A detailed description of local population structure in Arabidopsis thaliana is presented, including an assessment of the genetic relatedness of individuals collected from the same field. A hierarchical sample of four individuals from 37 local populations, including North America, England, Eastern and Western Europe, and Asia, and a selection of ecotypes, were analysed for variation in Adh, ChiA, FAH1, F3H, Rpm1, Rps5, and five microsatellite loci. Twenty-eight of the 37 population samples contained individuals with identical multilocus haplotypes, 12 of which were fixed for a single haplotype. These monomorphic populations were evenly distributed over the species range. Only in North America did we find a single multilocus haplotype shared among different populations, perhaps indicating a continental founder event. Despite the occurrence of local inbreeding, a considerable amount of genetic variation was found segregating within and among local populations. A novel analysis of haplotype differences reveals that genetic differentiation occurs at every geographic scale in A. thaliana, where we find a surprising under-representation of recent migrants between local populations. This leads us to hypothesize that most dispersal between A. thaliana populations is by pollen rather than seed. Based on the structure of A. thaliana populations, it appears that regional groups of local populations may provide the most appropriate genetic material for linkage disequilibrium mapping of adaptive traits. [ABSTRACT FROM AUTHOR]

Abstract Previous studies have shown that the major metabolic resistance locus in the insecticide-resistant Drosophila line Rst(2)DDT Wisconsin maps between the markers cn and vg on chromosome 2. Six cytochrome P450 genes exist in this region. We investigated the expression levels of these P450 genes in DDT-resistant and -susceptible fly lines. We report: (i) DDT resistance is significant (> 30-fold) and dominant, (ii) resistance is reduced by the cytochrome P450 inhibitor PBO, (iii) there is constitutive over-expression relative to susceptible flies of two genes encoding cytochrome P450 enzymes within the cn-vg region (CYP6G1 = 4.3-fold; CYP12D1 = 6.0-fold), and (iv) exposure to DDT results in an increased expression of only one of these two P450 genes (CYP12D1 ≥ 6-fold above constitutive resistant fly baselines). [ABSTRACT FROM AUTHOR]

Studies the alcohol dehydrogenase (Adh) cline of Drosophila melanogaster on the east coast of the United States. Latitudinal cline in the frequencies of two common alleles at the Adh locus; Significant clinal differentiation; Selection responsible for the cline; `Selective equivalence' test; Combined insertion/deletion polymorphism.

DNA sequence variation in a 1.1-kb region including the coding portion of the Tpi locus was examined in 25 homozygous third-chromosome lines of Drosophila melanogaster, nine lines of Drosophila simulans, and one line of Drosophila yakuba. Our data show that the widespread allozyme polymorphism observed in cosmopolitan D. melanogaster is due to a glutamic acid substitution occurring in a phylogenetically conserved lysine that has been identified as part of the "hinged-lid" active site of the enzyme. This observation suggests that the replacement polymorphism may have important functional consequences. One replacement polymorphism was also observed in D. simulans, although its functional relevance is more difficult to assess, since it affects a site that is not strongly conserved. This amino acid change in D. simulans is associated with a single lineage possessing seven unique silent substitutions, which may be indicative of balancing selection or population subdivision. The absence of fixed amino acid differences between D. melanogaster and D. simulans and only a single difference with D. yakuba suggests that triose phosphate isomerase is under strong functional constraint. Silent variation is slightly higher for D. melanogaster than for D. simulans. Finally, we outline the general lack of evidence for old balanced polymorphisms at allozyme loci in D. melanogaster. [ABSTRACT FROM PUBLISHER]

Proposes a simple statistical test of the neutral protein evolution hypothesis based on a comparison of the number of amino-acid replacement substitutions to synonymous substitutions in the coding region of a locus. Compares DNA sequences of the coding region of the `Adh' locus in three species in the `Drosophila melanogaster' species subgroup.