Geiger-Thornsberry Gretchen L, Mackay Trudy F C
Department of Genetics, North Carolina State University, Raleigh 27695, USA.
Genet Res. 2002 Jun;79(3):211-8. doi: 10.1017/s0016672302005621.
The nature of forces maintaining variation for quantitative traits can only be assessed at the level of individual genes affecting variation in the traits. Identification of single-nucleotide polymorphisms (SNPs) associated with variation in Drosophila sensory bristle number at the Delta (Dl) locus provides us with the opportunity to test a model for the maintenance of variation in bristle number by genotype by environment interaction (GEI). Under this model, genetic variation is maintained at a locus under stabilizing selection if phenotypic values of heterozygotes are more stable than homozygotes across a range of environments, and the mean allelic effect is much smaller than the standard deviation of allelic effects across environments. Homozygotes and heterozygotes for two SNPs at Dl, one affecting sternopleural and the other abdominal bristle number, were reared in five different environments. There was significant GEI for both bristle traits. Neither condition of the model was satisfied for Dl SNPs exhibiting GEI for sternopleural bristle number. Heterozygotes for the abdominal bristle number SNPs were indeed the most stable genotype for two of the three environment pairs exhibiting GEI, but the mean genotypic effect was greater than the standard deviation of effects across environments. Therefore, this mechanism of GEI seems unlikely to be responsible for maintaining the common bristle number polymorphisms at Dl.
维持数量性状变异的力量的本质，只能在影响性状变异的单个基因水平上进行评估。在Delta（Dl）位点鉴定与果蝇感觉刚毛数量变异相关的单核苷酸多态性（SNP），为我们提供了一个机会，来测试一个通过基因型与环境相互作用（GEI）维持刚毛数量变异的模型。在这个模型中，如果杂合子的表型值在一系列环境中比纯合子更稳定，并且平均等位基因效应远小于等位基因效应在不同环境中的标准差，那么遗传变异在稳定选择下会在一个位点上得以维持。对Dl位点上两个SNP的纯合子和杂合子进行了研究，其中一个影响腹侧板刚毛数量，另一个影响腹部刚毛数量，它们在五种不同环境中饲养。两种刚毛性状都存在显著的GEI。对于腹侧板刚毛数量表现出GEI的Dl SNP，该模型的两个条件均未得到满足。对于表现出GEI的三对环境中的两对，腹部刚毛数量SNP的杂合子确实是最稳定的基因型，但平均基因型效应大于效应在不同环境中的标准差。因此，这种GEI机制似乎不太可能是维持Dl位点常见刚毛数量多态性的原因。
