Gene structure and action in relation to heterosis

Abstract

The working hypotheses proposed for the interpretation of heterosis in terms of gene action can be reduced to two essential types. One is that of interaction between non-allelic genes; the other that of interaction between alleles. Examples of both types of action are, of course, known in physiological genetics. But while many examples of gene interactions have been analyzed in biochemical terms, only two of ‘one-gene heterosis’ have been so analyzed: sickling in man (Pauling, Itano, Singer & Wells 1949), and pab in Neurospora (Zalokar 1948). Physiological genetics does not provide any crucial argument to choose between a model of heterosis based on gene interactions and one based on allele interactions. Furthermore, advances in our knowledge of gene structure and action in recent years have led to the realization that there may be no absolute distinction between alleles of one gene and alleles of different genes. If this is so, the distinction between the two types of models for heterosis is one which has no longer a precise meaning, though it may still be useful at certain levels of approximation.