Inbreeding and Heterosis

The inbred-hybrid system remains as the most important breeding scheme for the commercial production of hybrid seeds. To accomplish the purpose of hybrid seed production two phenomena are inevitably involved as the genetic framework toward the exploitation of genetic effects: inbreeding and heterosis. This chapter presents a review on inbreeding and heterosis concepts and their values for a better understanding of the inbred-hybrid system for hybrid seed production. Inbreeding is a mating system in which matings occur between relatives (consanguineous mating). Heterosis is the genetic expression of the superiority of a hybrid in relation to its parents. It also depends on dominance and dominance types of epistatic effects; in this sense no heterosis can be detected for a quantitative trait in a hybrid, in relation to the average of the parents, if genes controlling the trait act in a strictly additive way (no dominance).