The creation of aneuploid families in the Pacific oyster, Crassostrea gigas thunberg

Aneuploidy is a chromosomal condition in which member chromosomes of the haploid set are present in an unequal number of copies. Such a condition provides a rare opportunity for genetic manipulation and analysis. Trisomics (2n + 1) and monosomics (2n - 1) for example, can be used for the identification and chromosomal assignment of important quantitative traits. Certain aneuploids may exhibit traits of commercial interest. In plants, 'complete sets of trisomic lines have been developed for all major crops. In mammalian livestock, aneuploids are lethal and of little value in genetic analysis and breeding. Studies in the pacific oyster have shown that many aneuploid conditions such as 2n - 1, 2n + 1, 3n -2, 3n - 1, 3n + 1, 3n + 2, 3n + 3, 4n - 2, 4n - 1 and 4n + 1, are viable. There are also preliminary indications that certain hypoploid conditions are superior in growth. However, comprehensive studies on aneuploids have not been possible due to the inability to create aneuploid oyster lines. Here we report the successful creation of five trisomic families in the Pacific oyster. Putative trisomic oysters were from a tetraploid group which was produced by inhibiting polar body I in eggs from triploids that had been fertilized by normal sperm. Oysters with an approximately diploid DNA content were distinguished from polyploids by flow cytometry and used for trisomic screening. Because biopsy of chromosome number is difficult in adult oysters, we used progeny testing of early embryos for chromosomal confirmation of parental trisomy. Twenty-five random crosses of putative trisomics were made, and five of them were confirmed to be trisomic families. The five trisomic families are being maintained for further evaluations, and more aneuploid families are being developed. Banding techniques and FISH probes are also being developed for chromosomal identification of trisomic families.