Chemical mutagens: alkylating agents. I: Genetical effects

Abstract

Tests for mutagenic effects of chemicals are almost as old as modern genetics (see article by Auerbach in Vol. 1 of ‘Chemical Mutagens’; Bibliography). In 1914, T.H. Morgan had already tried to produce mutations in Drosophila by treatment with alcohol and ether, but without success. In the twenties and thirties, Muller’s techniques for the determination of mutation rates in Drosophila (Chapter 5) were applied to a variety of chemicals. Russian workers claimed success for ammonia, iodine, potassium permanganate and copper sulphate; for the last-named substance, confirmatory data were published in U.S.A. In most of these experiments, the differences between the frequencies of sex-linked lethals in controls and treated flies were statistically significant, but treatment effects were small. Lethal frequencies in the treated series rarely exceeded or even reached 1%, which is roughly the upper limit for untreated flies. A fact that was not known at the time but meanwhile has been clearly established, is the dependence of spontaneous mutation frequency on breeding procedure and on the brood tested (1). This raises the possibility that the chemicals used in these early experiments had yielded increased mutation frequencies not by inducing mutations but by affecting the rate of sperm utilization in such a way that the samples from treated males contained a higher proportion of mutationbearing spermatozoa than did those from the control flies.