Cytological Basis of "Sex Ratio" in Drosophila pseudoobscura

Abstract

Cytological investigations of both laboratory and wild "sex ratio" lines of Drosophila pseudoobscura reveal that, contrary to earlier reports, no extra replication of the X chromosome occurs in primary spermatocytes. Normal disjunction of the sex chromosomes at anaphase I leads to equal numbers of X-bearing and Y-bearing secondary spermatocytes. In the latter, the Y chromosome regularly shows a "degeneration" at second anaphase. The "sex ratio" effect can be explained in terms of regularly nonfunctional products of meiosis.