Dosage of the maternal effect gene associated with the tumorous-head abnormality in Drosophila melanogaster.

The penetrance of tuh-3 observed in the progeny of triploids with two doses of tuh-1 was not statistically different from that occurring in the progeny of their diploid sisters with two doses. A higher penetrance was observed in the progeny of triploids with three doses of tuh-1 than in the progeny of their diploid sisters with two doses. These observations suggest that the maternal effect responsible for increasing the penetrance of tuh-3, the gene causing the tumorous-head abnormality, is caused by a specific gene product of tuh-1, the maternal-effect allele. In addition there is probably a maternal-effect threshold, lying between amounts produced by one and two doses of tuh-1, below which no increased penetrance of tuh-3 is observed.