Studies on mutation at esterase loci in Drosophila virilis. III. Genic variation in Est-.ALPHA. alleles produced by mutation experiments.

Abstract

With the highly polymorphic Est-a locus of Drosophila virilis, enquiry was made into its genetic structure.Electrophoresed were 1.47 x 106 progeny raised from heterozygous females comprising thirty-two varieties of genotypes. In this study, 65 mutants were found to occur. Fifty-nine of these covered the full range of variation commonly observed in natural populations in Japan, whereas the remaining six were rather novel and in possession of new alleles not formerly recorded. Such a novelty in the behavior of the relevant genes may be understood as to indicate the occurrence of intragenic recombination.It has been suggested that the gene in question has some specific recombination sites, the regions of some intervening inert parts of genes (introns) or, if any, coding regions (exons) having a possible, specific base sequence where recombination is unaccompanied with base correction of the unpaired bases. Granting that intragenic recombination chiefly occurs within the region of introns, the most probable model is discussed to satisfactorily explain these results.

Contribution of recombinants produced by female flies heterozygous forEst-α alleles to genie variation ofDrosophila virilis

“…Since I reported earlier the detection of 65 recombinants from among about 1-47 xlO 6 progenies (Tsuno, 1985), the addition of the present data mean that a total of 20x 10 6 alleles at the Est-a locus of D. virilis has been examined, from which 83 recombinants in all were obtained.…”

“…Female flies heterozygous for each of the 12 alleles just mentioned were crossed with Est-a. 0 males and their progenies were electrophoresed according to the procedure described earlier (Tsuno, 1981(Tsuno, , 1985. Since most electrophoreses in my experiments were carried out on homogenates each comprising two progenies in order to accelerate the experimental procedure, the appearance of the null allele could not be detected inevitably in such a case.…”

“…In order to avoid taking a fly with denatured enzymes as a true a 0 one, only the case of appearance of one active /?-band and no active a-band on the electrophoregram of a progeny was classified as an occurrence of the null allele. The number of examined progenies was about 4 x 10 4 flies in each cross, because this number had proved to give a reliable statistical discrimination of recombination frequency in such a study (see Tsuno, 1985). Then additional experiments were carried out for previous crosses that had yielded fewer than 4 x 10 4 progenies, that is, Cross Nos.…”

“…Then additional experiments were carried out for previous crosses that had yielded fewer than 4 x 10 4 progenies, that is, Cross Nos. F17, F21, and F22 in Tsuno (1985), because of the difficulty in statistical analysis. Unfortunately, some of those previously used strains had been lost, so newly established strains a 1 ' 4 and a' 16 , having the same electrophoretic mobility as the previous ones, were tested.…”

“…locus of D. virilis, as a representative of the former, is highly polymorphic and has high genetic heterozygosity (Tsuno, 1975;Tsuno, Aotsuka & Ohba, 1984). Alleles of this locus, moreover, can produce mutants different from the parental allele types by a putative intragenic recombination in female heterozygotes (Tsuno, 1985), but neither in homozygotes nor in male heterozygotes. So, we shall hereafter refer to these 'mutants' as 'recombinants'.…”