Chromosome inheritance in triploid Pacific oyster Crassostrea gigas Thunberg

Abstract

Reproduction and chromosome inheritance in triploid Pacific oyster (Crassostrea gigas Thunberg) were studied in diploid female  triploid male (DT) and reciprocal (TD) crosses. Relative fecundity of triploid females was 13.4% of normal diploids. Cumulative survival from fertilized eggs to spat stage was 0.007% for DT crosses and 0.314% for TD crosses. Chromosome number analysis was conducted on surviving progeny from DT and TD crosses at 1 and 4 years of age. At Year 1, oysters from DT crosses consisted of 15% diploids (2n ¼ 20) and 85% aneuploids. In contrast, oysters from TD crosses consisted of 57.2% diploids, 30.9% triploids (3n ¼ 30) and only 11.9% aneuploids, suggesting that triploid females produced more euploid gametes and viable progeny than triploid males. Viable aneuploid chromosome numbers included 2n þ 1, 2n þ 2, 2n þ 3, 3nÀ2 and 3nÀ1. There was little change over time in the overall frequency of diploids, triploids and aneuploids. Among aneuploids, oysters with 2n þ 3 and 3nÀ2 chromosomes were observed at Year 1, but absent at Year 4. Triploid progeny were significantly larger than diploids by 79% in whole body weight and 98% in meat weight at 4 years of age. Aneuploids were significantly smaller than normal diploids. This study suggests that triploid Pacific oyster is not completely sterile and cannot offer complete containment of cultured populations.

Reproductive effort and growth in Crassostrea gigas: comparison of young diploid and triploid oysters issued from natural crosses or chemical induction

“…On the other hand, other studies have shown that the production of fully mature gametes in triploid Pacific oysters is greatly reduced compared to diploids, i.e. between 2 and 13% of diploid female oocyte production (Guo & Allen 1994c, Gong et al 2004.…”

“…Environmental variation probably also contributes to variability of reproductive effort estimators published for triploid Pacific oysters (Allen & Downing 1986, Shpi-gel et al 1992, Guo & Allen 1994c, Gong et al 2004. Further comparative studies of triploid versus diploid performances should be made under different environmental conditions (i.e.…”

Transcriptomic Profiling of Gametogenesis in Triploid Pacific Oysters Crassostrea gigas: Towards an Understanding of Partial Sterility Associated with Triploidy

“…Such non-sterile triploid oysters have been named triploid alpha (3nα) oysters, differentiating them from those producing only a few gametes called triploid beta (3nβ) [20]. Interestingly, gametes of triploid oysters can reach functional maturity [23] and when fertilized, can develop into some viable progeny, though the proportion of aneuploids is high [23], [24].…”

Cytogenetic evidence for diversity of two nuclei within a single diplomonad cell of Giardia

“…In four isolates studied, we found two dominant karyotype patterns in which the two nuclei differ in one and two chromosomes, respectively. Occurrence of minor karyotype variants in each Giardia isolate conforms to a usual frequency of artifacts of a spreading technique used for chromosome preparations (Gong et al 2004;Rosenbusch 2004). Both statistical evaluation of karyotype distribution and approximately the same rate of variation in the isolates (three noncloned, geographically distinct isolates and the cloned line WB-1B) suggest that also in Giardia, the minor variants represent the artifacts.…”