A genetic sexing strain of a mosquito, Anopheles quadrimaculatus, Species A, was synthesized for the preferential elimination of females during the egg stage. Malathion susceptibility was used as a conditional lethal, and the dominant malathion-resistance allele was linked to the Y chromosome via a radiation-induced reciprocal translocation involving the terminal end of the right arm of chromosome 3 and the Y chromosome. Examination of mitotic chromosomes and salivary polytene chromosomes revealed the precise nature of the translocation. Genetic leakage, through recombination, in the strain was very low (0.02%).