ABSTRACT
In Mendel's original experiments, the two allelomorphic forms of the genes used were related to one another as dominant and recessive. That is, one of the pair, the dominant, came to complete expression in the heterozygote, suppressing all signs of the other recessive gene. This relationship is not a necessary one; all gradations are known between cases in which the heterozygote shows the full effect of one gene (complete dominance) and cases in which the heterozygote is strictly intermediate and it is impossible to speak of either gene as dominant. A considerable degree of dominance is, however, much more usual than would be expected on a basis of pure chance, and several attempts have been made to explain why this should be; they are considered later (p. 297).
