Comparison on chromosome stability between inbred and outbred full-sib families of tetraploid Crassostrea gigas by cytogenetic technique

The building of the superior tetraploid strains is the key to the development of the oyster triploid industry. The tetraploids with abnormal chromosome number are often not conducive to the further breeding of its new strain. Inbreeding, which occurs frequently in artificially selected populations, is equally likely to occur in artificially induced tetraploid oysters. To explore the differences on chromosome stability between the inbred and outbred tetraploids of Crassostera gigas, 22 full-sib families with inbreeding coefficient of 0 (F0), 0.25 (F1) and 0.375 (F2) were built to compare the distribution and frequency of chromosome number of tetraploid cells. From the cellular level, the chromosome number of embryonic cells and somatic cells in all families mainly varied from 30 to 40, and with most cells containing 40. Of all the aneuploid cells observed, most of them contain 38 and 39 chromosomes. From the individual level, both the proportions of aneuploidy and mosaic individuals in inbred lines increased, maximally up to 13.89% and 27.78%, respectively. From the family level, the distributions of cell chromosome number in the inbred families were more dispersed than that in line F0. The aneuploidy rates of embryonic cells in inbred lines F1 and F2 were 6.3% and 19.5% higher than that in the outbred line F0, respectively. The rates of somatic cells were 11.3% and 15.5% higher than that in line F0. These results indicate that continuous inbreeding of tetraploid oysters may decrease their chromosome stability.