Theoretical studies on mechanism of maintenance of genetic variation at the DNA level

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Natural populations have a large amount of genetic variation at the DNA level. How much and why such genetic variation is maintained in a population is one of the most important questions in population genetics. In this research project, I have worked on this subject and obtained the following results.In order to understand the mechanism of maintenance of DNA polymorphism, we have to measure the amount of DNA polymorphism accurately. There are several statistical methods for estimating the amount of DNA polymorphism. Many of them, however, cannot be used when selective constraints are different among different sites. In this research project, I have developed a new statistical methods for estimating the amount of DNA polymorphism, which can be used even when selective constraints are different among different sites. I have also obtained a new statistical methods for estimating the amount of DNA polymorphism from AFLP data.When a natural selection is operating on a particular site, we cannot use the neutral theory. I have works on the effect of natural selection on the amount and pattern of DNA polymorphism. One of interesting results is that even when a natural selection is operating on a particular site, we can still estimate the amount of DNA polymorphism in terms of 4Nv, where N is the effective population size and v is the mutation rate. Furthermore, we can estimate the ancestral DNA sequence of the DNA sequences sampled from a population. I have also studied the effect of population structure on the amount of DNA polymorphism.