Discriminatory Effect of Ultra-Violet Rays on Mutation in Drosophila

Abstract

THE discovery that rearrangements of genes in Drosophila produce ‘position effects’ like the effects of ‘gene mutations’, and that such rearrangements may be so minute as to be practically indistinguishable cytologically or genetically from gene mutations¹ has raised the question whether there is any essential distinction between so-called gene rearrangements and gene mutations, or whether the latter are to be regarded merelyas special cases, at the extreme lower limit of size, of the former. This question, fundamental both to problems of genetics and of the biological action of radiation, has recently become more acute since it has become known that, although gross rearrangements vary in frequency as the 3/2 power of the number of ions produced by X-ray irradiation^2,3,5 (indicating that they commonly involve the reunion of chromosomes broken at twoor more separated points by separate ionizations or activations), minuterearrangements, like ‘gene mutations’, vary directly as the number of the ions^4,5 (indicating that two breaks near together may result from one ionization or activation).