What can be learnt about selection from gene frequency distribution?

Polymorphism has been studied at the Esterase 6 locus in the Yellow Fever mosquito Aedes aegypti (L.) in laboratory stocks. At least 12 alleles are present, with up to four coexisting in a stock. The allele frequency distribution is quite sharply peaked at a mode of about 0.25. The experimental data are compared with the results of simulation based on two models, one in which the initial global distribution is taken to be the stationary distribution obtained from the neutral model assuming M = 4 mu Ne = 1 and the other in which the initial global distribution is generated from the experimental populations studied. The results suggest that the patterns observed are not likely to arise through random fluctuation of frequencies in neutral alleles, but that some kind of selection maintains polymorphism, either in the wild or in the laboratory, or both.