EFFECTIVE POPULATION SIZE AND GENETIC DRIFT PLAYING MAJOR ROLE IN THE INCREASE OF A WILD TYPE ALLELE IN COMPETITION TO A MUTANT ALLELE IN DROSOPHILA MELANOGASTER

摘要

An experiment was conducted to see the distribution of wild and mutant flies (black bodied) in small and large populations, initiated by equal ratio of wild type and black bodied flies of Drosophila melanogaster. The small populations were raised in food vials and large populations in food bottles. It was observed that populations established in food vials with few numbers of individuals experienced drastic decline in the number and were totally exterminated from the vials in just 4-5 generations than those established by larger numbers of individuals in food bottles. Since the founded members contained wild types as well as black body mutants, a perusal was also made to analyze whether both types of flies equally survived. The results indicated that natural selection favored wild types than mutants leading to very quick elimination of mutants from the culture medium. The quick disappearance of mutants in the early generations from the culture vials might have occurred due to selection of wild types and in further generations the unavailability of any fly from the culture vials could be attributed to a number of reasons, and one being accumulation of deleterious genes due to inbreeding. Thus the effective population size is one of the forces for the survival and perpetuation of a species. It was found that genetic drift in small founded population lead to female biased sex ratio in subsequent generations while in large founded population equal sex ratio was obtained. Female biased sex ratio in small founded populations can be explained by Local Mate Competition theory.