Apparent Double Crossing-Over in a Short Genetic Interval in Drosophila melanogaster

Abstract

IN view of the reported occurrence of double crossing-over within a short genetic interval in Aspergillus ¹ and of the purported existence of negative interference in bacteriophage², it is worth while to record the recovery in Drosophila melanogaster of apparent double cross-over types within a short genetic interval where interference is nominally expected to be complete. These double cross-overs were found incidentally to a study of pseudo-allelism at the white (w) loci³. The relevant genetic interval extends from the X-chromosome loci of yellow body colour (y) to split bristles (spl), mutants of which served as markers for the study of crossing-over between w pseudoalleles. The standard map distance for this interval is commonly given as three units, a value at least twice as great as more recent measurements indicate⁴. Throughout this study, parental females were always made heterozygous for the autosomal inversions Cy and Ubx ¹³⁰. These inversions serve to increase crossing-over strikingly in the y-spl interval to values varying from 5 to 11 units⁵.