Abstract
Drosophila melanogaster males carrying a ring‐X (Xc2) and a doubly‐marked Y chromosome (BSYy+) were treated with methylmethane sulfonate (MMS) and procarbazine, and mated with repair‐deficient mei‐9a females or ordinary repair‐proficient females. Observed (recovered) chromosome loss were scored and nonrecovered inferred. Ring‐X loss based on shifts in sex ratio were noted. Results indicate that the mei‐9a female is a strong potentiator of chromosome loss induced by MMS and procarbazine in line with the effect recently shown for dimethylnitrosamine (DMN)‐induced chromosome lesions (Zimmering, et al 1980.