Restricted selection and effective population size

A simple and flexible selection method, 'restricted truncation selection', has been developed to screen superior individuals from populations with family structure. 'Restricted' means placing limits on the contributions of families to the selected group and on the number of families allowed to contribute. Selection is made on the basis of individual performance judged by phenotype or breeding value estimate. Formulae have been derived to predict the approximate effective population size in the selected group. Changes in the restrictions used modify the distribution of family contributions and thus lead to different effective sizes in the selected population. Effective size is influenced by sib type, heritability, selection intensity, initial family number and size. It is decreased by restrictions on the family number but increased by restrictions on family contributions. The application of the predictions of effective sixes to planning a breeding population is discussed.