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SUMMARY: To obtain useful information about the mechanism of the induction of gynogenesis in the Pacific abalone, nuclear behavior in normal and gynogenetic eggs was examined during meiosis and first cleavage. After its incorporation into the egg cytoplasm, the UV-irradiated sperm nucleus gradually dispersed and eventually developed into the male pronucleus, behaving like a normal sperm until contact with the female pronucleus. At mitotic prophase, the male pronucleus in the gynogenetic eggs did not form chromosomes like the female pronucleus, but became a dense chromatin body, which did not participate in karyokinesis. At completion of cytokinesis of the first cleavage, the UV-irradiated sperm nucleus was seen in the cytoplasm of one of the two blastomeres near the cleavage furrow. As a clear haploid mode was observed in the frequency distribution of chromosome numbers in gynogenetic larval cells, it is suggested that the paternal genome in the gynogenetic eggs does not contribute to the next generation.

Effects of ultraviolet (UV) irradiation on genetic inactivation and morphological structure of sperms were examined in the scallop, Patinopecten yessoensis . Haploid gynogenesis of the scallop was successfully induced by 50–60 s UV irradiation of 720 μW cm −2 s −1 . The fertilization rate apparently decreased with increasing irradiation time, and the development of the eggs fertilized with the genetically inactivated sperms terminated before reaching the D-shaped larvae stage. Scanning electron microscopy (SEM) showed clear destruction of the sperm acrosome and flagellum in the UV-irradiated sperms. As the duration of UV irradiation increased, the acrosome of sperms tended to suffer greater damage, until the sperms eventually lost their flagella. Abnormalities in these structures have appeared to account, at least in part, for the decline of the fertilization rate of eggs inseminated with UV-irradiated sperms.

SUMMARY: Effects of ultraviolet (UV) irradiation on genetical inactivation and morphological features of sperm were examined in the Pacific oyster. Ultraviolet light (254 nm) was effective for inactivating sperm chromosomes. Irradiation for 60 s at a UV intensity of 72 erg/mm 2 per s was the optimum dose to achieve haploid gynogenesis. The rates of the fertilization and the development of D-shaped larvae decreased with increasing irradiation time, and the development of the eggs fertilized with the genetically inactivated sperms terminated before reaching the D-shaped stage. Electron microscopy showed clear destruction of the sperm acrosome and flagellum in the UV-irradiated sperms. As the duration of irradiation increased, the acrosome of sperms tended to suffer greater damage until the sperms eventually lost their flagella. Abnormalities in these structures have appeared to account, at least in part, for the decline of the fertilization rate of eggs inseminated with UV-irradiated sperms.