ABSTRACT
Heterosis arises when divergent strains are crossed and generally the more divergent the strains, the greater the heterosis. Heterosis depends for its existence on dominance and is associated with heterozygosity. Since genes are ultimately expressed as physiological characters, the genetic basis of heterosis can be explained in terms of measurable physiological differences between the parent breeds. One example of heterosis that is used commercially, particularly in subtropical regions, is the higher productivity of Boa indiaus x Bos taurus crossbreds compared with the parental breeds. A three-breed rotation, which makes maximum theoretical use of both individual and maternal heterosis, magnifies even further the problem of finding suitable breeds to use in the cross. The amount of heterosis that arises in crosses of different cattle breeds can be measured as the difference in performance of the F1 hybrid form: the mean performance of the parental breeds; the performance of the more productive parent; or the performance of the F2 generation.
