THE NEGATIVE CORRELATION BETWEEN SOMATIC ANEUPLOIDY AND GROWTH IN THEOYSTER CRASSOSTREA-GIGAS AND IMPLICATIONS FOR THE EFFECTS OF INDUCED POLYPLOIDIZATION

This study extends previous observations that chromosome loss in somat ic cells of juveniles of the pacific oyster Crassostrea gigas is assoc iated with reduced growth rate. All four studies designed to examine t his association (two using random population samples and two using ful l sibs) produced the same result. This consistent effect appears to be unrelated with the commonly, but not consistently, observed correlati on between degree of allozyme heterozygosity and growth. We propose th at the inverse relationship between aneuploidy and growth is due to th e unmasking of deleterious recessive genes caused by 'progressive hapl oidization' of somatic cells. Because unmasking of deleterious recessi ve genes by random chromosome loss is unlikely in polyploid cells, thi s hypothesis may also provide an explanation for the observation that artificially produced polyploid shellfish usually grow at faster rates than normal diploid ones.