Studies on fused, a mutant gene producing ovarian tumors in Drosophila melanogaster.

Flies homozygous for the mutant gene fused (fu) are characterized by fused wing veins, a maternal effect upon embryogenesis, and ovarian tumors. A number of mutant alleles have been studied and all exhibit this same syndrome. The rate at which ovarian tumors develop is characteristic for each allele. This rate was shown to be independent of modifying genes and unaffected by the maternal cytoplasm. The rate is also temperature-sensitive, tumors appearing more slowly at 18 than at 25 degrees C. Females heterozygous for all possible combinations of these alleles were produced, and, in all 21, tumors were observed in the compound females. Cases of dominance, complementarity, and interference were observed with reference to certain allelic combinations. A model is proposed to explain the diverse effects on development of the fused gene and also the interaction of the alleles in ovarian development. Females homozygous for fused and either heterozygous or homozygous for the second chromosomal recessive gene female-sterile (fes) were also studied. The fes gene was shown to be epistatic to fu in fu/fu; fes/fes females, and the rate of tumor production was greater in fu/fu; fes/+ females than in fu/fu; +/+ females. A mechanism for the action of fu and fes in controlling cell division is presented.