Identification of cytoplasmic factor inhibiting the Y-sperm maturation and cytogenetical analysis of spermatogenesis.

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A strain which exhibits an extreme sex ratio has been isolated from a wild population. The strain was originally reported to carry an cytoplasmic factor which is transmitted materhally and causes sex ratio distortion through in the males bearing the cytoplasm. We therefore examined the effect of an antibiotic, aging, mitochondrial DNA, cytoplasmic RNA and transplantation of the cytoplasm on the sex ratio distortion in order to identify the cytoplasmic factor, but could not support the original description. However we have found a sex ratio mutation on the X chromosome of the Drosophila simulans strain. The gene named paternal sonless (psl) is located at about 30 in map distance and has not been known in any species belonging to the Drosophila melanogaster species complex. Cytogenetical studies revealed as follows; The psl males show a high frequency of chromosome bridges at meiosis, especially at the second division, which resulting in multi-nuclear spermatocytes and spermatids. Almost every abnormal spermatid has a mass of fluorescent positive chromatin at the site of cytokinesis. The abnormal spermatids are mostly discarded from sperm cysts in the maturation process. Only normal sperms, which are consisted of largely X-sperms, get matured.