Genetic polymorphisms in Drosophila.

摘要

In a population evolving by gradual change, the amount of genetic variation is important because the rate of evolution is absolutely limited by the degree of genetic variability. Various forces of evolution such as natural selection, random genetic drift and migration operate on genetic variability which provides the raw material for evolution. Thus the rate of evolution is absolutely limited by the amount of genetic variability already existing in the population. The basic parameters of evolutionary genetics are: (a) the amount of genetic variation measures the evolutionary potential of a population at a given time, and (b) the amount of genetic differentiation between populations reflects the operation of evolutionary processes since the divergence of populations from the common original population. Extensive work has been done on a variety of organisms to estimate the degree of genetic variability in natural populations at the level of chromosome, allozyme and DNA. The results of these studies have shown that there exists a considerable degree of genetic variability although there are interspecies-specific and intraspecies-specific variations in the degree of genetic polymorphism. Drosophila, a dipteran insect commonly known as fruit fly, occupies a unique status among the species which have been used for this kind of research. It was used for the first time in 1905 by Carpenter for experimental studies and in 1909 by Morgan for genetic studies. Since then it has served as a good biological model for different types of studies such as genetics, behaviour, evolution and development. The present review summarizes briefly the work done on genetic polymorphism with particular reference to chromosome, allozyme and DNA polymorphism in Drosophila, with a brief discussion on balanced polymorphism, genetic coadaptation, linkage disequilibrium and genetic hitch-hiking, which are of considerable evolutionary significance.