Cytological studies on artificially induced gynogenesis in the Pacific abalone

To obtain useful information about the mechanism of the induction of gynoge nesis in the Pacific abalone, nuclear behavior in normal and gynogenetic eg gs 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 ma le pronucleus in the gynogenetic eggs did not form chromosomes like the fem ale pronucleus, but became a dense chromatin body, which did not participat e 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 bla stomeres near the cleavage furrow. As a clear haploid mode was observed in the frequency distribution of chromosome numbers in gynogenetic larval cell s, it is suggested that the paternal genome in the gynogenetic eggs does no t contribute to the next generation.