Oysters Non-aneuploidy Preparation And Biological Characterization

Aneuploids are organisms where member chromosomes of the haploid set arerepresented in unequal copies. Mollusks like plants and unlike most vertebrate speciescan tolerate a variety of aneuploid conditions. In this study, aneuploids were preparedwith diploid, triploid crossing, and the research has been done on the isolation andidentification of the aneuploid Pacific oyster (Crassostrea gigas) by fluorescence insitu hybridization (FISH) and isozyme analysis. At the same time, we studied thetypes, frequency and survival of aneuploids as well as their growth, trying to explaindifference of growth between aneuploids and diploids with bioenergetics analysis.The results of this study are listed as followings:1. Chromosome number analysis was conducted on surviving progeny from diploid female × triploid male (DT) and reciprocal (TD) crosses of Pacific oyster at one and four years of age. And the frequency of aneuploids was different in the two crosses: (1) There are more aneuploids in DT crosses. At Year 1, oysters from DT crosses composed of 17.5% diploids (2n=20) and 82.5% aneuploids that consisted 75% 2n level and 7.5% 3n level. At Year 4, there was no change in evidence. 16.4% diploids and 83.7% aneuploids were found. Aneuploids included 81.6% 2n level and 2.1% 3n level. No triploid was found in both ages. (2) In contrast, oysters from TD crosses consisted of more euploids (88.1%) and some aneuploids (11.9%). There was little change over time in the overall frequency of aneuploids, but the ratio of triploids increased from 30.9% to 41.2%, while that of diploids decreased from 57.2% to 47.1%. - 120 -巩宁 牡蛎非整倍体的制备及其生物学特性研究 中国科学院研究生院博士学位论文 (3) Diploids and triploids crossing is an effective method to prepare aneuploids in mollusks. Triploid females produced more euploid gametes and viable progeny than triploid males. The study suggested that triploidy is not an evolutionary dead end and may play a role in chromosome number evolution in mulluscs.2. Viable aneuploid chromosome numbers included 2n+1,2n+2,2n+3,3n-2 and 3n-1. Oysters with 2n+2 and 2n+3 chromosome were found at the first time. The absence of chromosome numbers between 24 and 27 suggests that they are lethal in the Pacific oyster. Oysters with 2n+3 and 3n-2 chromosomes were observed at Year 1,but absent at Year 4 due to some individuals dead or chromosomes loss. The proportion of oysters with 2n+2 chromosomes was decreased at Year 4. But as a group, the survival of aneuploids was similar as that of euploids.3. The Pacific oyster trisomy 10 was successfully identified with the aid of ITS1, ITS2 rDNA probe that was prepared with PCR amplify. Trisomy 10 from DTA1, DTA3 and AA groups were screened out by fluorescence in situ hybridization (FISH). Isozyme analysis was carried out with starch gel (SGE) and polyacrylamide gel (PAGE) electrophoresis in aneuploid Pacific oysters. In the locus of MDH-1, two aneuploids showed the expected bands, which can be used for the chromosomal mapping of isozyme gene when the extra chromosome of aneuploids was identified by FISH technique.4. Chromosome number influenced the growth significantly in Pacific oysters at both Year 1 and 4. Triploidy progenies were significantly larger than diploids by 79% in whole body weight and 98% in meat weight at four years of age. On the other hand, aneuploids were significantly smaller than normal diploids with almost all the growth parameters as a group. Oysters with 2n+2 chromosomes were smaller than other aneuploids. There was considerable variation in body size within each chromosome number group, especially in trisomy. The bioenergetics analysis suggested that triploids spent more energy for growth than diploids and aneuploids did, while aneuploids cost less energy for...