The number and distribution of esterase 6 alleles in populations of Drosophila melanogaster

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Abstract
High resolution electrophoretic analyses of the polymorphic esterase 6 enzyme have been carried out on 133 isoallelic lines from three Australian populations of Drosophila melanogaster spanning 25° of latitude. These and previous data for 157 lines from another Australian population at an intermediate latitude reveal a total of 14 polymorphic esterase 6 allozymes, falling into five major mobility classes. Two classes, EST6-F and EST6-S, contain eleven of the allozymes but one allozyme, EST6-8 within the EST6-S class, is several times more common than any other. Variation in the frequency of this single allozyme can explain most of the latitudinal clines previously reported for the major EST6-F and EST6-S classes. Thermostability analyses of 52 of the Australian lines and 13 American lines reveal at least seven more EST6 variants within five of the allozymes, bringing the total number of variants to at least 21. Of the six allozymes for which more than one line was subjected to thermostability analyses, only EST6-8 could not be partitioned into additional variants. This corroborates a previous finding that two different isolates of the Est6-8 allele have identical DNA sequences and suggests that this allele, although now the most common, has nevertheless arisen relatively recently.