Wrinkling of the eye in hybrids between Drosophila virilis and Drosophila lummei is caused by interaction of maternal and zygotic genes.

Hybrids of Drosophila virilis females and Drosophila lummei males have visible developmental anomalies in external adult structures. Reciprocal hybrids are normal, and the anomalies are not found in other interspecific F1 hybrids of the virilis subgroup. Antibiotic treatments with ampicillin, streptomycin and tetracycline did not cure the syndrome. The genetic basis of the wrinkling of the compound eye was analysed in detail. Both male and female F1 progeny of D. virilis mothers were affected, indicating that wrinkling of eyes is maternally determined. F1 hybrid females produced healthy progeny. Backcross hybrid females (D. virilis x F1) with 16 different combinations of autosomes, either heterozygous or homozygous for D. virilis, were crossed with D. lummei males. It was found that homozygous D. virilis chromosomes 2 and 5 together were necessary to induce the maternal effect. The hybrid zygote responded to the maternal effect when the chromosomes 2, 4 and/or 5 were heterozygous. Elimination of the small sixth (dot) chromosome of D. lummei from the hybrids was correlated with the wrinkling of eyes, but was not the cause, as the two phenomena had a different genetic basis and temperature response. Furthermore, the eyes were wrinkled in flies which presumably had had no D. lummei dot chromosome to lose.