Accumulation of Lethals and Suppression of Genetic Load in Irradiated Populations of Drosophila melanogaster

Abstract

Populations carry their load of mutations. It is considerably increased by increased exposures to environmental mutagens. This is considered the most serious consequence of such mutagens in the long run (Morton et al., 1956). Genetic load means that the optimal fitness for any genetic locus is reduced by mutations that are deleterious if heterozygous and/or homozygous. The concept of genetic load has been developed by Muller (1950). He has employed it to underscore his urgent warnings against the enormous genetic hazards by the invisible ionizing radiations. It took two decades from Muller’s first proof of the mutagenic action of X-rays (Vth International Congress of Genetics, Berlin, 1927; see Muller, 1927, 1928a,b) to his winning the Nobel prize (after the explosion of atomic bombs raised public interest). It took another two decades until public interest and legislation began to center on artificial radiation sources and their potential dangers and still another decade to initiate the almost total ban on radiations that governs present-day politics. A focus of the argumentation was the dangerous in-crease in genetic load. The concept of genetic load, its necessity, and its limits have been outlined by Wallace (1970) in an excellent monograph. Experimental evidence on load and on viabilities came mainly from work on Drosophila (Bonnier et al., 1958, 1959; Carson, 1964; Cordeiro et al., 1973; Eiche, 1972; Falk, 1967; Kratz, 1975; Marques, 1973; Sankaranarayanan, 1964, 1965; Salceda, 1967; Wallace, 1956, 1958, 1963) with some additional data from mammals [see Green (1968) for a review]. These data have not been substantially enlarged since then, but have been revisited with interesting new views (Wallace, 1989; Wallace and Blohowiak, 1985a, b).