The Timing of Temperature Sensitivity of Leaky Fertility Factor Mutations in Male DROSOPHILA MELANOGASTER.

Some of the mutations of the male fertility factors on the Y chromosome give rise to a small proportion of fertile males, each of which produces only a small number of progeny. Many of these mutations are temperature-sensitive, producing a larger proportion of fertile males at 25 degrees C than at 19 degrees C. One of these mutants was carefully analyzed and it was found that only sperm which mature in the first five days of adult life can effect fertilization, regardless of the temperature regimen. A unique temperature-sensitive period was localized to the mid-pupal stage by single twenty-four-hour 25 degrees C treatments applied at various times in the life cycle to flies otherwise grown at 19 degrees C. The temperature sensitivity associated with this pupal sensitive period is adequate to account for all of the difference in fertility between flies grown continuously at the two temperatures. The timing of the temperature-sensitive process in combination with a cytological study of spermiogenesis indicates that temperature sensitivity occurs after the first meiotic metaphase during a spermatid stage. Thus it affects some post-transcriptional event in the expression of the phenotype of the fertility factor.