Interacting effects of sodium monohydrogenarsenate and selenocystine on crossing over in Drosophila melanogaster.

Abstract

Drosophila melanogaster females of X chromosome genotype y cυ υ f/++++ were reared as larvae on 16-treatment media, representing the various combinations of four concentrations each of sodium monohydrogen arsenate and selenocystine (concentrations were 0, 2, 10 and 50 μM). The fourfold replication of selenocystine curves at four arsenate levels confirmed the existence of a selenocystine effect indicated earlier (Ting and Walker, 1969), as well as the segmental differences in and reversibility of the effect. A marked "sink" in crossing over was found both in total single exchange chromosomes and total double exchange chromosomes at 10 μM selenocystine and peaks in single exchange for segment 1 and for the whole chromosome and for double exchange for segments 1 and 2 at 2 μM were noted. In addition, arsenate was shown to exert a marked effect in the selenocystine-concentration region 0-10 μM; crossover frequencies were quite consistently increased by arsenate treatment at zero selenocystine, and considerable differences were introduced into the initial region (0-2 μM) of selenocystine segmental curves by arsenate treatment, with resultant increases in total single exchange and double exchange curves. In addition, the general effect was noted in arsenate-concentration curves, at 2 and 10 μM As: a drop in double exchange and an increase in single exchanges. Hypotheses are presented relating these effects to possibilities regarding the incorporation of selenocystine and arsenate into chromosomal protein and DNA respectively.