Wageningen University & Research, P.O. Box 338, 6700 AH, Wageningen, The Netherlands.
Norsvin SA, Storhamargata 44, 2317, Hamar, Norway.
Genet Sel Evol. 2023 Jan 13;55(1):2. doi: 10.1186/s12711-022-00773-z.
The genetic correlation between purebred (PB) and crossbred (CB) performances ([Formula: see text]) partially determines the response in CB when selection is on PB performance in the parental lines. An earlier study has derived expressions for an upper and lower bound of [Formula: see text], using the variance components of the parental purebred lines, including e.g. the additive genetic variance in the sire line for the trait expressed in one of the dam lines. How to estimate these variance components is not obvious, because animals from one parental line do not have phenotypes for the trait expressed in the other line. Thus, the aim of this study was to propose and compare three methods for approximating the required variance components. The first two methods are based on (co)variances of genomic estimated breeding values (GEBV) in the line of interest, either accounting for shrinkage (VC) or not (VC). The third method uses restricted maximum likelihood (REML) estimates directly from univariate and bivariate analyses (VC) by ignoring that the variance components should refer to the line of interest, rather than to the line in which the trait is expressed. We validated these methods by comparing the resulting predicted bounds of [Formula: see text] with the [Formula: see text] estimated from PB and CB data for five traits in a three-way cross in pigs.
With both VC and VC, the estimated [Formula: see text] (plus or minus one standard error) was between the upper and lower bounds in 14 out of 15 cases. However, the range between the bounds was much smaller with VC (0.15-0.22) than with VC (0.44-0.57). With VC, the estimated [Formula: see text] was between the upper and lower bounds in only six out of 15 cases, with the bounds ranging from 0.21 to 0.44.
We conclude that using REML estimates of variance components within and between parental lines to predict the bounds of [Formula: see text] resulted in better predictions than methods based on GEBV. Thus, we recommend that the studies that estimate [Formula: see text] with genotype data also report estimated genetic variance components within and between the parental lines.
纯系（PB）和杂交系（CB）表现的遗传相关([Formula: see text])部分决定了在亲代系中对 PB 表现进行选择时 CB 的反应。先前的一项研究使用亲本纯系的方差分量，包括例如表达在母系之一中的性状的父本系的加性遗传方差，推导出了[Formula: see text]的上限和下限的表达式。如何估计这些方差分量并不明显，因为来自一个亲本系的动物没有表现在另一个系中表达的性状的表型。因此，本研究的目的是提出并比较三种方法来近似所需的方差分量。前两种方法基于感兴趣的系中的基因组估计育种值（GEBV）的（协）方差，要么考虑收缩（VC），要么不考虑（VC）。第三种方法直接使用单变量和双变量分析（VC）的约束最大似然（REML）估计值，而忽略方差分量应指感兴趣的系，而不是表达性状的系。我们通过比较这三种方法在猪的三向杂交中五个性状的 PB 和 CB 数据估计的[Formula: see text]与预测的[Formula: see text]之间的关系，验证了这些方法的有效性。
在 15 个案例中，有 14 个案例使用 VC 和 VC 时，估计的[Formula: see text]（加或减一个标准误差）介于上限和下限之间。然而，VC（0.15-0.22）的范围比 VC（0.44-0.57）小得多。使用 VC 时，估计的[Formula: see text]在 15 个案例中只有 6 个案例介于上限和下限之间，范围从 0.21 到 0.44。
我们得出结论，使用亲本系内和系间的 REML 估计方差分量来预测[Formula: see text]的界限比基于 GEBV 的方法产生了更好的预测。因此，我们建议那些使用基因型数据估计[Formula: see text]的研究也报告亲本系内和系间的遗传方差分量估计值。
