Interstrain heterochromatin polymorphisms in Drosophila melanogaster.

Neuroblast chromosomes of 16 Drosophila melanogaster laboratory stocks (15 wild type and 1 carrying the mutant vermillion) were carefully analyzed for Q-banding patterns and morphological characteristics, in all the mitotic phases. Two forms of intraspecific heterochromatin variations, involving three types of chromosomes, are described: 1) differences in the fluorescence pattern with regard to the Y chromosome and the centromeric heterochromatin of the pair II; 2) differences in the size of the heterochromatic segment of the X chromosome. An unambiguous evidence of such variants was obtained by comparing homologous chromosomes in the F1 hybrids, as well as in the F2 offspring, where differences in appearance of the heteromorphic chromosomes was readily identified as to the parental origin. The possible evolutionary significance and the usefulness of such cytologically detectable genetic differences between various strains, are considered.