Dominigenes of the Vestigial Series in Drosophila Melanogaster.

T IS almost axiomatic in studies of developmental genetics that the action I of a particular gene cannot be described completely without reference to the residual genotype or “general genic environment” (term proposed by TSCHETWERIKOFF 1926). It is also generally agreed that “all factors probably partake of the nature of modifiers, since each factor appears to affect many characters and to alter the expression of other factors” (SINNOTT and DUNN 1932). The widespread acceptance of these concepts has led to the frequent assumption of the presence of modifiers on general grounds without a serious attempt to define the genetic basis more precisely. Modifiers whose presence has been only vaguely determined have even played an important role in certain theoretical generalizations. particularly in the field of evolutionary genetics. Few studies have been made with a view to a precise analysis of the genetics of a system of modifiers. T.he present investigation is an extension of one very thorough analysis of this type of situation-that is, the effect of a series of genetic modifiers on heterozygotes bearing the normally recessive gene vestigial in Drosophila melanogaster.