The Interaction of Genes in Development.

Since it has been shown that the transmission of most hereditary traits can best be explained on the theory of the gene, it is important to try to trace the relation between particular genes in the fertilized egg and the correlated somatic manifestations that appear during development. That such correlations do exist has been abundantly demonstrated, but just how the gene exerts its effect on the soma is still unknown. As a first step towards an analysis of this problem one may inquire into the interrelation between the genes themselves. Here there are two possibilities to be considered: (1) that the genes interact with each other to give the cell its structural and functional characteristics; (2) that each individual gene separately exerts its own specific influence.

These alternatives may be illustrated by the following schemata, in which A and B represent the genes in a cell whose contribution to the soma may be either S or S′ (depending on such factors

as topographical relations, stimuli, etc.). In (1) all the interaction between A and B is in the nucleus and N is the single resultant effect—a particular type of protoplasm. This would seem to correspond to a common conception among experimental biologists. In (2) A and B are more or less independent, n, n′ and n″ representing distinct elements in the total of cytoplasmic potentialities. In this case it is not the genes themselves, but certain of their secondary products that interact, so that while A ultimately affects both S and S′, B affects only one of them. The determination of which of these alternatives is in accord with the true situation is of considerable importance to the understanding of protoplasmic reactions in general.