Quantitative Genetics of Heterosis

In this chapter, the authors review basic quantitative genetic concepts in heterosis, introduce the concept of baseline heterosis, review the results of over 50 years of gene action studies, and suggest needs for future research. They feel that the quantitative genetics of heterosis must be tied to plant improvement and that any theory of heterosis must explain and be consistent with the increase in yield of hybrid maize since 1930. Inbreeding depression is the converse of heterosis. Measured genotypes using a combination of Cockerham's analysis and J. M. Cheverud and E. J. Routman's analysis, may be one of the best tools for understanding epistasis and its contribution to heterosis. Much of the quantitative genetic theory of heterosis is based on single locus theory. Single locus heterosis theory assumes the absence of epistasis, which considerably simplifies the mathematics and interpretations of the theory. Gene action and gene effects have been extensively studied in many crop species.