Transient Linkage Disequilibrium in Drosophila

THE results of some applications of biochemical techniques to population genetics apparently contradict certain basic tenets of evolutionary theory. Thus by the use of gel electrophoresis for soluble proteins, to estimate genetic variation within natural populations, levels of variability much greater than those predicted by the genetic load theory have been found1–3. Second, the rate of allele substitution calculated from data on amino-acid substitutions in the primary structures of certain homotogous proteins4 turns out to be two or three orders of magnitude greater than the productions of the genetic load theory for species of the appropriate evolutionary separation. Among the explanations so far proposed for these discrepancies are the selective neutrality per se of numerous isoallelles4,7–9, frequency dependent selection10,11 and selectively maintained linkage disequilibria12–14. Although there have been many theoretical discussions of linkage disequilibria12–14, experimental evidence of their frequency and importance in natural populations has been sparse15,16. We now describe a transient linkage disequilibrium between two allozyme loci in a laboratory population of Drosophila melanogaster