An effect of x-rays on crossingover in drosophila

Abstract

In Drosophila melanogaster when a white-eyed, long-winged female is crossed with an eosin-eyed, miniature-winged male, the daughters are all heterozygous and may be represented by the formula , indicating that one of the × chromosomes carries the determiners for white eye-color (w) and long wings (M) while the other carries the determiners for eosin eye-color (W^e) and miniature wings (m). If such a heterozygous female is bred she will have four kinds of regular sons irrespective of the male with which she is crossed, since the regular sons obtain their × chromosomes from their mother only. In two of the kinds of sons the characters will appear as they entered in the original cross, i. e., one kind will be white-eyed and long-winged and the other eosin-eyed and miniature-winged; these make up the noncrossover classes. In the other two kinds of sons the characters will be interchanged, i. e., one kind will be white-eyed and miniature-winged and the other eosin-eyed and long-winged; these make up the crossover classes. It is usual in work on crossingover to cross the heterozygous females with a recessive male, which in this case would be white-eyed and miniature-winged, in order that the daughters may also show the crossover and noncrossover classes. The experiments to be described were designed primarily to test for nondisjunction and for that reason the females were mated to males with the dominant character red-eyed so that the exceptional sons and daughters could be recognized. This did not of course affect the character of the regular sons and it is from counts of these that the crossover values have been determined. No attempt has been made to correct the data for double crossingover.