Cytological Basis of "Sex Ratio" in <i>Drosophila pseudoobscura</i>

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.