| Artificially induced gynogenesis, as one of the latest techniques in morden genetic breeding, refers to the development in which involves fertilization of eggs with geneticcally inactivated sperms and chromosome-doubling during either meiosis I , II or the first cleavage using physical or chemical shock treatment. It shows great potential in genetic improvement and getting new species of aquatic animals, especially rapid production of inbred lines. In addition, gynogenesis is also important to settle many genetic problems including examining sex-determination, gene mapping, gene-centromere recombination, clones, In this paper, the inductive parameters to produce gynogenetic diploids in the scallop, Chlamys farreri, were optimized and its cytological changes of eggs during fertilization and early development were observed in two methods. The results obtained in this study are as follows:1. Gynogenetic diploids in Chlamys farreri were induced by ultraviolet (UV) light irradiation and 6-DMAP treatment. The geneticcally inactivated sperms generated by the UV rays (254nm) at intensity of 800 uw/cm2s for 50 s were used to fertilize with normal eggs to produce haploid gynogenesis. Then fertilized eggs were treated with different concentration (40~80mg/L) of 6-DMAP for 10, 15, 20 min respectively at 30~40min after insemination at 20℃ water temperature when 20-30% of eggs released the first polar body under an optical microscope. In order to find out the best combination of concentration and duration, diploid percentage and survival rate of D-larvae were examined by chromosome distributions, flow cytometry analysis and counting the D-larvae. The results showed that the optimal combination of 6-DMAPof concentration and duration was to treat fertilized eggs by 60 mg/L 6-DMAP for 20min, resulting in 57.6% diploid rate and 22.25% survival rate of D-larvae. The diploid rate of selected group examined by flow cytometry was 57.3%, in accordance with the 54% diploid rate on the basis of counting chromosome.2. Nuclear behaviors of gynogenetic dipoid eggs of Chlamys farreri were observed carefully under a fluorescence microscope during fertilization and early development. According to cytological observation, the ultraviolet-irradiated sperm nucleus also expanded in a wide rang after penetrating into eggs and some of them developed into male pronucleus, but there were no fusion of the two pronuclei. At metophase of the first cleavage, the male pronucleus had no chromosomes, unlike the female pronucleus, but became a dense chromatin body (DCB), which did not participate in the karyokinesis at mitotic anaphase and located between the two maternal chromosomes. At completion of the first cleavage, DCB was seen either in the region of the first cleavage furrow as two partitioned parts or in the cytoplasm of one of the two blastomeres. During the second cleavage, the experience of DCB is fundamentally identical to the first cleavage. Treatment with 6-DMAP inhibited effectively the segregation and suppression of chromosomes, blocking the formation and release of the second polar body and resulting in a big diploid female pronucleus.3. To treat normal and gynogenetic diploid eggs of Chlamys farreri with fixing in Bouin's fixative, making paraffin section, staining by hematoxylin-eosin, their nuclear changes were observed carefully under an optical microscope during fertilization and early cleavage. The results indicated that the female and male pronuclei of normal eggs fused into zygotonuceus, but the behaviors of gynogenetic diploid eggs were extremely complicated. The sperm nucleus of gynogenesis had at least two situations: One was that it kept dense all along and couldn't develop into male pronucleus. Another was that it expanded again after the second meiosis but didn't reach its maximum as a normal male pronucleus. In the process of the first and secondcleavage, the sperm nucleus of gynogenesis did not participate in the karyokinesis and located between the two maternal chromosomes. At completion of the cleavage, DCB was seen either in the region of the cleavage furrow or in the cytoplasm of one of the two blastomeres. Treatment with 6-DMAP, the formation of the second polar body was inhibited and diploid female pronucleus was formed. In addition, the phenomena of poly sperm and poly spindles in the experiment are also observed and analyzed.
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