Mechanisms of Inbreeding Depression and Heterosis for Profitable Dairying

Genes in diploid organisms operate singly, in pairs, and in conjunction with genes at other locations throughout the nuclear DNA. Inbreeding depression and heterosis arise from the effects of gene combinations, that is, the effects of pairs of genes. Gene pairs are unique characteristics of individuals that are broken down and reformed each generation. This basic biological fact, introduced to many of us in high school biology, is the foundation of everything there is to say about this topic. Very few topics are so well rooted in a simple process. Simplicity suffers, however, under real-world challenges of combining breeds or selecting to improve within a pure breed under a multi-trait breeding objective. This paper attempts to explain in a rudimentary way the ways in which genes interact, transmit, and recombine and the implications of those processes to breeding options available to dairy farmers.