The Genetic Consequences of Anaphase Bridge Formation in Drosophila.

ROSSING over between ring and normal X chromosomes of D. melunoc gaster was first studied by L. V. MORGAN (1933); the later work of STURTEVANT and BEADLE (1936) provided an understanding of the behavior of anaphase bridges resulting from crossing over in inversion heterozygotes. The present work represents an attempt to interpret the data from ring/rod heterozygotes using the rules derived from inversion heterozygotes by the above workers, with emphasis on a discrepancy between the observed and expected frequencies of that class of gamete with no X chromosome, the nullo-X class. It will be shown that this discrepancy, a deficiency of the nullo-X class, occurs also in experiments involving certain types of X inversion heterozygotes, and the bearing of the phenomenon on the nature of chromatid separation will be discussed.