Abstract
Burnt (Bu) is a dominant mutant which appeared in the offspring of the pupae treated with X-rays. In F2 generation of burnt, much more than 25% of the total eggs are inviable and the segregating ratio of burnt to normal is about 2:1. It is assumed that the homozygous individuals for Bu are perfectly killed in the embryonal stage. These lethal embryos live so long as the setae are completely formed. They can, however, never enter reversion and all die away. Imperfect formation of amnion on the dorsal direction, and no-closing of the “Rücken-naht” and of the mid-gut seem to check the further development. The function of the gene Bu, when homozygous, appears at the stage between elongate and reversional.
