Veränderlichkeit des chromosomalen polymorphismus beiDrosophila subobscura

Abstract

In order to determine whether chromosomal inversion polymorphism inDrosophila subobscura is stable or varies from season to season, samples from selected sites were taken and analyzed at regular intervals. In 1960 the descendants of 749 females from samples collected at four sites in five months were examined. In 1963 and 1964, samples weretaken from only two sites at three seasons (spring, summer, autumn). Each of the twelve samples totalled 60 males which were then individually crossed with females from the “Küsnacht” stock, homozygous for the standard sequences. Eight descendant larvae from each cross were analyzed.

Samples were judged according to the following criteria: a) Occurrence and frequencies of gene arrangements; b) Occurrence and frequencies of hetero- and homokaryotypes for each chromosome; c) distribution pattern of polymorphism over the entire set of chromosomes (shown in diagram of heterokaryotypes).

Our results show that between samples from 1963 and 1964 there are yearly, seasonal and local differences in karyotype. The starting frequency of heterokaryotypes in the spring of one year differed from that of the next. Both frequencies increased from spring to autumn. At the same time the standard sequences which appear more frequently on each chromosome than any other gene arrangement, decrease during the summer in favour of other arrangements.

In our 1960 material we found that karyotypes differed from locality to locality. These differences, however, were only statistically significant in a few cases. Furthermore, these figures show a less regular fluctuation than those of the other two years. The varying results for the first year and the second two may be due to differences in the size of our samples; further to secondary effects brought about by the use of different methods, and possibly to actual differences in the sampled populations.