Knowing the phenotypic variance and the selected proportion allows us to determine the superiority of the selected parents (how much better than average the selected parent are) on forehandbeforehand. This is based on the variance and the selected proportion only, so before the actual animals have been identified. This is very convenient! We can use this information to predict the genetic response to selection, given a certain proportion. This response can then be evaluated, and, if desired, compared to predicted selection results when using a larger or smaller selected proportion. The selection intensity is an important tool in the decision making process.
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