The DNA content of sperm of Drosophila melanogaster

Karyotypes are described of diploid and tetraploid R. ficaria with particular reference to the variation in structure and size of their SAT-chromosomes. In four wild populations of tetraploid R. ficaria an excessive enlargement of the satellite region is present on the short arm of one of the four SAT-chromosomes and is described in detail. The unusual and irregular behaviour of this body in the form of bridges and fragments at mitotic anaphase is outlined and an attempt is made to explain it in terms of delayed or incomplete replication in heterochromatic segments. The whole process is discussed with reference to allocycly, subchromatids, a breakage fusion cycle, and B-chromosomes