Abstract
The question is posed whether karyotype frequencies in the active fraction of Drosophila subobscura populations vary consistently in the course of a day, or in accordance with weather changes. Significant daily variation occurred in all chromosomes with the exception of the sex chromosome. The proportions of the karyotypes Ust/1+2 and Ist/st decreased from early to late morning and increased during the evening. Ist/1 displayed a complementary behaviour. The homokaryotypes Ost/st and Est/st decreased both during the morning and the evening. Weather disturbances caused a remarkable variation in the frequencies of the standard gene arrangements.
