Inbreeding and heterosis

Discusses the effect of various levels of inbreeding (self-fertilization, sib matings, half-sib matings, cousin marriages) upon making heterozygous genes homozygous with the consequent loss of vigor. Presents data for the increased risk of genetic defect from cousin marriage in studies of phenylketonuria, of a Japanese population and a French population. The concept and estimation of lethal equivalents are given. Shows how increases in heterozygosity increase vigor (heterosis); hybrid vigor in corn in described in detail. Lecture given by Dr. J. F. Crow.