| Gynogenesis refers to the development of eggs fertilized by genetically inactivated sperm. Compared with classical genetic methods, the production of gynogenetic diploids offers the possible applications of the techniques in genetic research as well as part of breeding technologies for genetic improvement including gene mapping, study of genetic sex-determination, gene-recombination and the rapid production of inbred lines, mono-sexual broods or clones. It provides a new way for genetic improvement of scallop culture and to get well-bred species. Optimum inductive parameters of the scallop were tested. Cytological process in induction were observed and described in this paper. The results of this study are listed as folio wings:1. Effects of ultraviolet (UV) irradiation on genetical inactivation and ultrastructure of sperm were examined in the scallop, Chlamys farreri. UV irradiation of sperm for 30 s at a UV intensity of 2561 μWcm-2s-1 was the optimum dose to achieve haploid gynogenesis on the basis of observations on fertilization rate of the eggs, chromosome constitutions and flow cytometry analysis of the larvae. The rates of the fertilization and the development of D-shaped larvae decreased with increasing irradiation time, while the survival rate of trochophore larvae became improved at UV exposure longer than 20 s, suggesting the presence of a "Hertwig effect" in the gynogenesis of C. farreri.2. Electron microscopy showed clear destruction of the acrosome, cytoplasmic membrane, nuclear envelope, mitochondrial cristae, and flagellum in the UV-irradiated sperms. Moreover, an irradiation duration of 30 s caused decondensation of sperm chromatin. Abnormalities in these structures might affect the ability of sperm to fertilize the eggs.3. Nuclear changes in normal and gynogenetic eggs of the scallop were examined under a fluorescence microscope during meiosis and fertilization. Haploid gynogenesis wasinduced by sperms, which were ultraviolet (UV)-irradiated for 30 s at an intensity of 2561 uWcm'V1. Although UV irradiation did not effect either meiotic maturation or the formation of the male and female pronuclei, their developmental progress was delayed. At metophase of the first cleavage, the male pronucleus in UV-irradiated sperms inseminated with the normal egg formed no chromosome, unlike the female pronucleus, but became a dense chromatin body (DCB), which did not participate in the karyokinesis at anaphase of the first cleavage. At completion of cytokinesis of the first cleavage, the DCB was seen either in the cytoplasm of one of the two blastomeres or on the equatorial plate as two partitional parts. Cytological evidence of the induction of gynogenesis in the scallop was demonstrated.4. The induction of gynogenetic diploids during meiosis II in the Zhikong scallop was attempted using the treatments of cytochalasin B (0.5 ug/ml; CB) and 6-dimethylaminopurine (60 ug/ml; 6-DMAP).(1) CB and 6-DMAP treatments were successfully induced by suppressing polar body II, producing 52.4% and 49.3% gynogenetic diploids, respectively. Compared with CB treatment, 6-DMAP treatment produced more expected D-shaped larvaes.(2) According to cytological observations, 6-DMAP inhibited both karyokinesis and cytokinesis, resulting in the formation of one big diploid female pronucleus with strong fluorescence, while CB inhibited cytokinesis, resulting in two female pronuclei formations. On the other hand, the UV-irradiated sperm nucleus developed into a male pronucleus as a normal sperm nucleus. However, the male pronucleus formed no chromosomes during the mitotic prophase, and did not participate in karyokinesis at mitotic anaphase; these findings suggest that gynogenetic diploids were induced in the scallop.5. Conditions required for the induction of gynogenetic diploid by suppression of first cleavage in the Zhikong scallop were examined using treatments of cytochalasin B (0.5 Hg/ml; CB) and 6-dimethylaminopurine (60 ug/ml; 6-DMAP).(1) Treatments with CB and 6-DMAP were effectiv...
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