Gene Number, Kind, and Size in Drosophila.

The literature on X-ray effects contains two fundamental ideas which, if combined, should offer a better understanding of the physical properties of the gene on the one hand, and of the mechanism by which X-rays affect living tissue on the other. The first of these ideas is due to CROWTHER. He interpreted the rates at which living cells are killed by X-rays as due to the destruction of a vital center within each of these cells. The second idea comes from MULLER’S demonstration that X-rays impinging on chromatin will produce new gene mutations which, in turn, lead to new heritable characters. In order that the problem may be sharply defined, we shall confine the discussion to data bearing upon the kind and size of the genes present in an animal organism. The approach lies in a knowledge of the physical characteristics of X-rays in relation to their biological effects and to the rates a t which these alterations are produced. This paper presents an analysis of this problem on data obtained from the treatment of Drosophila sperm with long wave-length X-rays of known energy. Sperm of the wild-type were chosen since they represent concentrated chromatin whose full effects under normal conditions are better understood than those of any other material.