Eisen E J, Hanrahan J P, Legates J E
Genetics. 1973 May;74(1):157-70. doi: 10.1093/genetics/74.1.157.
Correlated responses to selection for postweaning gain in mice were studied to determine the influence of population size and selection intensity. Correlated traits measured were three-, six- and eight-week body weights, litter size, twelve-day litter weight, proportion infertile matings and two indexes of reproductive performance. In general, the results agreed with observations made on direct response: correlated responses in the body weight traits and litter size increased as (1) selection intensity increased and (2) effective population size increased. Correlated responses in the body weight traits and litter size were positive in the large population size lines (16 pairs), as expected from the positive genetic correlation between these traits and postweaning gain. However, several negative correlated responses were observed at small population sizes (one and two pairs). Within each level of selection intensity, traits generally associated with fitness tended to decline most in the very small populations (one and two pairs) and in the large populations (16 pairs) for apparently different reasons. The fitness decline at the small effective population sizes was attributable to inbreeding depression. In contrast, it was postulated that the fitness decline at the large effective population size was due to selection moving the population mean for body weight and a trait positively correlated genetically with body weight (i.e., percent body fat) away from an optimum.
为了确定群体大小和选择强度的影响，对小鼠断奶后生长性能选择的相关反应进行了研究。所测量的相关性状包括3周龄、6周龄和8周龄时的体重、窝仔数、出生12天时的窝仔体重、不育交配比例以及两个繁殖性能指标。总体而言，结果与对直接反应的观察结果一致：体重性状和窝仔数的相关反应随着以下因素增加：（1）选择强度增加；（2）有效群体大小增加。在大群体规模品系（16对）中，体重性状和窝仔数的相关反应为正，这与这些性状与断奶后生长性能之间的正遗传相关性预期一致。然而，在小群体规模（1对和2对）中观察到了一些负相关反应。在每个选择强度水平内，通常与适应性相关的性状在非常小的群体（1对和2对）和大群体（16对）中下降最为明显，原因明显不同。小有效群体大小下适应性的下降归因于近亲繁殖衰退。相比之下，据推测大有效群体大小下适应性的下降是由于选择使群体体重均值以及与体重在遗传上呈正相关的一个性状（即体脂百分比）偏离了最优值。
