Studies On Biological Characteristics Of Gynogenetic Diploids In The Chlamys Farreri And Crassostrea Gigas

Artificial gynogenesis involves induction of a haploid development by insemination with genetically inactivated sperm and diploidization of the female chromosome complement in order to produce viable diploid gynogenetic offspring. 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 mollusks and to get well-bred species.In this study, biological characteristics of gynogenetic diploids in the Chlamys farreri and Crassostrea gigas is analyzed. The results obtained in this study are as follows:1. The induction of gynogenetic diploids during meiosis II in the C. farreri was attempted using the treatment of 6-dimethylaminopurine (6-DMAP), and the biological performance in early survival and growth was also examined. The rates of cleavage, survival at the early embryo stage, the development of D-larvae, and survival on day 3, 6, 9, 12, 15 and 18 post-hatching were significantly lower than those in the control groups. Compared with that of normal diploids, the size of gynogenetic diploids was similar before day 3 post-hatching, but became bigger significantly after day 3 post-hatching. This suggests that following the elimination of the lethal recessive genes for the homozygosity, the performance of gynogenetic diploids in growth gradually became superior to that of the control.2. Inheritance of 8 microsatellite loci was examined in3 families of gynogenetic C. farreri produced by fertilizing eggs with UV irradiated sperm followed by inhibition of the secondmeiotic division. The proportion of heterozygo- usprogeny was used to estimate marker-centromere (M-C) distances. All loci conformed to Mendelian segregation in the control crosses when null alleles were accounted for. The absence of paternal alleles confirmed the gynogenetic origin of the offspring and indicated 100% success for 3 families. Estimated recombinant frequencies ranged from 0.40 to 0.64, which is lower than those observed in other gynogeneticdiploid animals. The mean recombination frequency was 0.53, corresponding to a fixation index of 0.47 in one generation. This is 2 times increase in homozygosity expected after one generationof sib mating (0.25), suggesting meiotic gynogenesismay be an effective means of rapid inbreeding in the scallop. M-C map distances for the 8 loci varied between 13 and 38 cM. The information about M-C distances will be useful for future gene mapping in C. farreri.3. The induction of gynogenetic diploids during meiosis II in the Pacific oyster C. gigas was attempted using the treatment of 6-DMAP, and the biological performance in early survival and growth was also examined. The rates of cleavage, survival at the early embryo stage, the development of D-larvae, and survival on day 3, 6, 9, 12, 15 and 18 post-hatching were significantly lower than those in the control groups. Compared with that of normal diploids, the size of gynogenetic diploids was similar before day 6 post-hatching, but became bigger significantly after day 6 post-hatching. This suggests that following the elimination of the lethal recessive genes for the homozygosity, the performance of gynogenetic diploids in growth gradually became superior to that of the control.