Associative Overdominance on the Pgm and Idh Locus Artificially Produced in Experimental Populations of Drosophila Melanogaster

Abstract

In the last decade population geneticists have learned that random processes influence much more the composition of populations than many might have thought before. Theoretical considerations led to the assumption that a great deal of the genetic variability found in natural populations must be selectively neutral (Crow and Kimura, 1970; Kimura, 1977; Nei, 1975). Yet, experimentalists, whenever they study any genetic trait which is variable in populations, observe in almost all cases clearly the effect of natural selection (Ayala and Anderson, 1973; Marinković and Ayala, 1975; Sperlich et al., 1975; van Delden et al., 1978; Pinsker, 1981). These seemingly contradictional results coming from theoretical considerations and experimental results are most probably due to the fact that theorists deal in their analyses with independent single gene loci, which do not exist in reality. Genes are always linked with other genes and interact with the genetic background. Selection is never directly acting on genes, even not on whole genotypes, but in the final analysis only on phenotypes.