Studies on mutation at esterase loci in Drosophila virilis. II. Intragenic recombination at the Est-.ALPHA. locus.

Abstract

In order to explore the mechanism of electrophoretic mutation due to intragenic recombination at the Est-a locus of Drosophila virilis, some selected alleles were repeatedly used in cross experiments.Some genotypes of female heterozygotes could produce several mutants, whereas others generated no significant number of mutants. Moreover, the directional nature of mutant occurrence was also confirmed as seen in the previous studies (Tsuno 1981). When newly arisen mutants obtained in the previous study were used in cross experiments, no increase in mutation rate was observed. From these observations, it is suggested that the majority of the mutations is due to intragenic recombination within introns rather than gene conversion. Thus, a general model for the Est-a locus is proposed.

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

“…After publication of two papers discussing the possibility of the exon-intron structure of the Est-a genes in Drosophila virilis (Tsuno 1981 and1982), corroborative investigation was conducted with about 1 X 106 progeny reared from various females heterozygous for different Est-a alleles in order to confirm the validity of the hypothesis.…”

“…With these alleles, half diallel crosses were carried out to obtain females heterozygous for them. Needless to say, homozygotes and heterozygous males do not produce any mutants (Tsuno 1981 and1982). In most, though not all, cases, the number of progeny collected from one genotype of heterozygous females for examination was about 4 X 104, because this number of flies is sufficient for statistical discrimination of such a low rate of mutation occurrence as seven mutants per 73,000 progeny [See F-16 in Table 2 (Tsuno 1982); P=0.047 by the method of Steel and Torrie 1960, pp.…”

“…In order to rightly relate these new variants to those known before, we were forced to change to a new system of grouping of Tsuno (1981) and Tables 2 and 3 of Tsuno (1982)). Alleles still undetermined are given in parentheses alleles on the basis of relative mobilities, designating the most common allele as the standard, a'°°.…”

“…It is of interest to note in addition that such mutations tend to occur in a specific direction; that is, mutant types obtained from a specific genotype of female heterozygotes are classified mostly into one or two specific types, though it should be possible for more than ten types of mutants to appear. This locus has been thus interpreted as consisting of a "split" structure of intron and exon sequences (Tsuno 1981 and1982).…”