A STUDY OF GENETICS OF DIELDRIN-RESISTANCE IN HOUSEFLY (MUSCA DOMESTICA L.)

Abstract

Reciprocal mass crosses and back-crosses were performed between two homogeneous strains of the housefly (Musca domestica L.), representing the extremes in susceptibility and resistance to dieldrin. The hetero-zygotes were found to be intermediate between susceptible and resistant parents, and showed no evidence of sex linkage or cytoplasmic effects. The F2 generation segregated in an approximate ratio of 1:2:1 into susceptible, heterozygote and resistant phenotypes, while the back-cross to the susceptible, parent yielded 49.8:50.2 susceptible: resistant males, and 48.8:51.2 susceptible: resistant females. Elimination of susceptible forms in the back-cross progeny by use of a discriminating dosage and interbreeding the survivors produced offspring segregating into 26% susceptible, 50.1% heterozygote and 23.9% resistant, in excellent statistical agreement with a ratio of 1:2:1 expected in simple Mendelian inheritance. It is concluded that resistance to dieldrin in the housefly strain studied is due primarily to a major single pair of alleles or to a number of closely linked alleles so that they are inherited as a single unit.