THE ISOLATION OF CROSSOVER SUPPRESSORS ON HOUSE FLY AUTOSOMES AND THEIR POSSIBLE USE IN ISOLATING RECESSIVE GENETIC FACTORS

Abstract

A test procedure was devised to isolate crossover suppressors on autosomes of the house fly, Musca domestica L. Adult males from a wild-type strain were X-rayed and mated to virgin females carrying two mapped markers on a particular chromosome. F1 females heterozygous for an unmarked test chromosome and a marker chromosome were then backcrossed to appropriate marker males and the F2 progeny scored for reduced recombination frequencies. Two suppressors were recovered for chromosome III using this technique. One suppressor was recovered for each of chromosomes II, IV, and V. Cytological analyses of testicular tissues from suppressor heterozygotes revealed unpaired regions or loop configurations between autosomal homologues of interest in each suppressor strain. Three of the suppressors were lethal in the homozygous condition. One suppressor homozygote was viable and fertile; one appeared to be viable but sterile. Intrastrain matings between suppressor heterozygotes were usually less fertile than intrastrain matings between wild-type males and females. Lowered egg hatches were almost always recorded in heterozygous suppressor outcrosses to wild-type flies. Male suppressor outcrosses were usually less fertile than their corresponding female outcrosses. The data indicate that the crossover suppressors can be used to isolate recessive genetic factors in the house fly.