Genetic analysis of selected strains of eastern oyster (Crassostrea virginica Gmelin) using AFLP and microsatellite markers

Amplified fragment length polymorphisms (AFLPs) and microsatellite markers were used to examine genetic variation and divergence in 4 selected strains (DBH, NEH, FMF, and CTS) and 1 wild population (DBW) of the eastern oyster Crassostrea virginica Gmelin. Eighty-six AFLP markers (from 3 primer pairs) and 5 microsatellite loci were used for the analysis of 30 oysters from each of the 5 populations. Microsatellite loci were considerably more variable than AFLPs. The observed heterozygosity ranged from 0.560 to 0.640 across populations for microsatellites, and from 0.186 to 0.207 for AFLPs. Both Fst and phiPT of microsatellite data and phiPT statistics of AFLP data revealed significant divergence between all pairs of populations. There was no significant reduction in heterozygosity in all 4 selected strains; however, the number of alleles per locus was considerably lower in the selected strains than in the wild population. Two strains subjected to long-term selection for disease resistance shared frequency shifts at a few loci, which deserve further analysis to determine if they are linked to disease-resistance genes.

Are paw preference differences in HI and LO mice the result of specific genes or of heterosis and fluctuating asymmetry?

Collins (1985) has described two separate mouse strains, obtained by selective breeding, which differ in having high (HI) or low (LO) degrees of paw preference on a standard test. In this paper I argue that the differences between these strains may not be due to a specific gene (or genes) but, instead, probably reflect differences in the total heterozygosity of the strains, such that the HI strain is more heterotic than the LO strain. Greater degrees of heterozygosity are argued to buffer against fluctuating asymmetry and hence result in a greater degree of paw preference.