DEPENDENCE OF THE ADAPTIVE VALUES OF CERTAIN GENOTYPES INDROSOPHILA PSEUDOOBSCURA ONTHE COMPOSITION OF THE GENE POOL

Abstract

In a previous publication (Levene, Pavlovsky, Dobzhansky, 1954) we have reported experiments on laboratory populations of Drosophila pseudoobscura in which three different gene arrangements were present among the third chromosomes. The adaptive values of six karyotypes (three inversion homozygotes and three heterozygotes) were estimated from the observed changes in the relative frequencies of the gene arrangements in the experimental populations. The results indicated that the adaptive values of at least some of the karyotypes were not constant; they depended upon the presence or absence of certain other karyotypes in the same population. Thus, individuals homozygous for the CH gene arrangement in third chromosome (CH/ CH) had a fitness apparently superior to AR homozygotes (AR/AR) in populations in which ST third chromosomes were also present, but CH/CH were inferior to AR/AR in fitness when ST chromosomes were absent. ST homozygotes (ST/ST) were superior to ST/CH heterozygotes in populations which also had AR chromosomes, but ST/CH were superior to ST/ST in the absence of AR. Lewontin (1955) reported some elegant experiments in which constant numbers of larvae of certain genotypes of Drosophila melanogaster were introduced