Genetic Consequences of Crossbreeding ''2

C ROSSBREEDING involves the mating of two or more breeds. In most species of domestic livestock, crossbreeding has some desirable consequences, especially in the production of market stock. These consequences are the production of heterosis, the opportunity to incorporate desirable genetic material quickly, and the chance to combine several desirable traits into a market animal. The consequences of crossbreeding depend on gene frequency differences among the breeds with the resulting increase of heterozygotes in the cross and the degree of dominance. For the crossbreeding to be utilized commercially in a class of livestock, there either must be a source of distinct genetic groups or the production of such groups must be economically possible, and the resulting crosses must have a distinct economic advantage over conventional market stock. Species having low reproductive potentials, such as cattle, must rely on exploiting the existing genetic differences among groups like breeds. Lucky is the species in which crosses among existing breeds have an economic advantage. The purpose of this paper is to describe the consequences of crossbreeding in genetic terms by using a simple model. This is done so that the factors influencing the consequences can be specified and used to develop crossbreeding programs that maximize the advantage.