The Developmental Mechanics of Hereditary Abnormalities in the Chick

Abstract

The problem of the mode of gene action in development can be approached in different ways. The geneticist will choose the genotype as the variable; he will select those cases in which the effect of a large number of genotypic variants on a single phenotypic character, for instance pigmentation, can be studied. Dr. Wright will presently discuss one of the most illuminating examples of this type. The embryologist will follow a different approach. He begins the analysis at the other end, at the phenotypic manifestations; he will attempt to trace backward, step by step, the chain of events from the established structural expressions towards the initial gene action. In doing so, he will apply his way of thinking and his methods. He is aware of the extremely complex interplay of actions and reactions between different parts of the developing embryo. He recognizes that any change in one part, at one moment, is reflected in many others, and the analysis of the mechanisms of such embryonic correlations is his domain. A gene-controlled modification of a developmental process will not only find expression in the primordium where it originates but in other parts as well.