Genetics of inbred Drosophila melanogaster. VII. Evidence of normal chromosome pairing in the distal ends of X-chromosomes in secondary non-disjunction.

Abstract

In tests of secondary non-disjunction in hybrids from two inbred lines (+w ++ H– K/y wa ex vf – 2IBS Yy+) the majority of exceptional females are phenotypically w/wa. 1252 such females were tested individually to reveal whether recombination had occurred or not. 30 of these females were recombinants, and 13 of them had recombined in the y-w region. A subdivision based on the brooding scheme indicated that in the 1–5th day broods the frequency of recombination in the y-w region was 0.49 % and in the 11–14th day broods 2.09 %. (The corresponding frequencies from XX mothers of the same inter-strain cross were 0.88 and 2.59 %, respectively.) It is concluded that these results are in accordance with a former analysis of phenotypic deviants among exceptionals, thereby indicating that recombination at the most distal end of the X-chromosome is very similar in XXY and XX females. The results also suggest near normal pairing in the most distal end of the X-chromosomes of XXY females prior to non-disjunction.