长牡蛎3代人工选育群体的微卫星分析

Genetic variability assessed by microsatellites in mass selection lines of Pacific oyster(Crassostrea gigas)

进行群体选育时,因近交机率增加和有效亲本数的减少,可能导致选育群体的遗传多样性下降,进而引起选育群体的性状衰退。为监测长牡蛎人工选育群体在选育过程中的遗传差异,实验应用微卫星DNA标记对长牡蛎野生和人工3代选育群体及其基础群体的遗传多样性进行了研究。微卫星10个位点在所有群体中均表现出较高的多态性,6个群体的平均等位基因数范围为24.0～29.7个,期望和观测杂合度分别为0.925～0.956和0.724～0.809。与野生群体和基础群体相比,长牡蛎选育3代群体的平均等位基因数和等位基因丰富度略有下降,但杂合度水平未发生明显变化。哈迪—温伯格平衡(HWE)检验结果显示,60个群体—位点组合中47个群体—位点组合显著偏离HWE平衡(P<0.05)。Fis指数均为正值,平均范围0.152～0.233,表明各群体在10个位点上表现为一定程度的杂合子缺失。各群体间Fst值的范围为0.008～0.025,遗传分化程度较弱。结果表明,连续3代的人工选育尚未明显降低长牡蛎群体的遗传多样性,仍可以一定的选择压力对选育群体进行人工选育,从而保证长牡蛎的优良生长性状得到持续提高。

In breeding industries, a challenging problem is how to keep genetic diversity over ensuing generations ,with the reason that a sufficient level of genetic variability is essential to maintain a sustained response from long-term selection for important traits. To investigate how mass selection process affects the genetic properties in our successive selection strains for fast growth of the Pacific oyster（ Crassostrea gigas）, ten polymorphic microsatellite loci were used to examine the genetic variation within population and differentiation among two wild populations,one base stock and three successive mass selection lines of C. gigas. High levels of genetic diversity of C. gigas in six populations were detected, as evidenced by large numbers of alleles per locus（ He = 24.0 - 29.7 ）, and high levels of heterozygosities（ Ho = 0. 925 - 0. 956 ,Ho = 0. 724 - 0. 809）. Compared with the wild and base populations of C. gigas,the mean allelic richness （Rs） in the three selectively bred generations declined slightly, but genetic heterozygosities were similar. Among the 60 population-locus cases（6 populations × 10 loci） ,47 cases deviated from Hardy-Weinberg equilibrium （P 〈 0.05）. Fst, values ranged from 0. 152 to 0. 233,resulting in heterozygote deficiencies at the ten loci in each population. Fst values ranged from 0. 008 to 0. 025, showing weak genetic differentiation among the populations. The results obtained in this study show that high genetic variation exists in the three generations of selective populations, and suggest that there is still potential for increased gains in future generations of C. gigas.