Genetic function correlated with unfolding of lampbrush loops by the Y chromosome in spermatocytes of Drosophila hydei

Summary

Deficiencies of the Y chromosome of Drosophila hydei including sites which develop lampbrush loops invariably cause sterility of males. Suppression of loop unfolding in one or more sites equally results in similar morphogenetic defects of spermiogenesis. A variegated type repression of lampbrush loop unfolding observed during the spermatocyte stage results in varying morphogenetic effects on spermiogenesis. This demonstrates the existence of causal relationships between the active phase of Y chromosomal factors in spermatocytes and the differentiation processes in spermatids.

In some translocated Y fragments the mode of unfolding of a particular pair of lampbrush loops may be permanently changed. As a result, lampbrush loops of a mutant phenotype are developed. Some alterations of this type are correlated with functional alterations resulting in defective spermiogenesis.

Three different fragments of the Y chromosome in which lampbrush loop formation was repressed have been tested for possible reversions of loop suppression by means of X irradiations. In none of the three cases reversion has been detected among two thousand tested chromosomes.