Assortative mating based on phenotype. II. Two autosomal alleles without dominance.

N the preceding paper ( SCUDO and KARLIN 1969), several one-locus models for I assortment based on the phenotypes with complete dominance were analyzed. Complete dominance is common for assortment on traits like color and pattern. Some cases are known, however, where some mating choice is based on chromatic traits determined by a single locus with other forms of interaction (SHEPPARD 1952). Assortment is also known to occur for other morphological and behavioral traits. The genetics of such traits is, however, not well developed up to the present time. This paper will be mainly concerned with assortment based on a pair of alleles where the heterozygote can be distinguished from both homozygotes. As in the first paper, we delimit a model by specifying the effects of a tendency to assort on the individual reproductive behavior and the fertility. We further restrict OUT consideration to the Gase in which the preference is manifested only in one sex. In most cases it does not matter which sex assorts but, for definiteness (reflecting the most common case in nature), the female is stipulated to be the assorting sex. Paralleling the development of the preceding paper, we shall be mainly interested in the direct evolutionary effects of assortment; the production of gene substitutions or the maintenance of partial genetic isolation between two ppulations. In contrast to the case of dominance, assortment for autosomal traits without dominance can also produce stable polymorphisms.