Weller Joel Ira, Shlezinger Meital, Ron Micha
Institute of Animal Sciences, ARO, The Volcani Center, Bet Dagan 50250, Israel.
Genet Sel Evol. 2005 Sep-Oct;37(5):501-22. doi: 10.1186/1297-9686-37-6-501.
Estimates of quantitative trait loci (QTL) effects derived from complete genome scans are biased, if no assumptions are made about the distribution of QTL effects. Bias should be reduced if estimates are derived by maximum likelihood, with the QTL effects sampled from a known distribution. The parameters of the distributions of QTL effects for nine economic traits in dairy cattle were estimated from a daughter design analysis of the Israeli Holstein population including 490 marker-by-sire contrasts. A separate gamma distribution was derived for each trait. Estimates for both the alpha and beta parameters and their SE decreased as a function of heritability. The maximum likelihood estimates derived for the individual QTL effects using the gamma distributions for each trait were regressed relative to the least squares estimates, but the regression factor decreased as a function of the least squares estimate. On simulated data, the mean of least squares estimates for effects with nominal 1% significance was more than twice the simulated values, while the mean of the maximum likelihood estimates was slightly lower than the mean of the simulated values. The coefficient of determination for the maximum likelihood estimates was five-fold the corresponding value for the least squares estimates.
如果不对数量性状基因座（QTL）效应的分布做出任何假设，那么从全基因组扫描得出的QTL效应估计值会存在偏差。如果通过最大似然法进行估计，并从已知分布中抽样QTL效应，则偏差应会减小。通过对以色列荷斯坦牛群的女儿设计分析（包括490个标记-父系对比），估计了奶牛九个经济性状的QTL效应分布参数。每个性状都得出了一个单独的伽马分布。α和β参数及其标准误的估计值随遗传力的变化而降低。使用每个性状的伽马分布得出的个体QTL效应的最大似然估计值相对于最小二乘估计值进行了回归，但回归因子随最小二乘估计值的变化而降低。在模拟数据上，名义显著性为1%的效应的最小二乘估计值的均值是模拟值的两倍多，而最大似然估计值的均值略低于模拟值的均值。最大似然估计值的决定系数是最小二乘估计值相应值的五倍。
