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

自然种群在DNA水平上存在着大量的遗传变异。在种群中保持这种遗传变异的程度和原因是种群遗传学中最重要的问题之一。在本研究项目中，我对这一课题进行了研究，取得了以下成果：为了了解DNA多态的维持机制，我们必须准确地测量DNA多态的数量。有几种统计方法可以估计DNA多态的数量。然而，当不同地点的选择性限制不同时，它们中的许多都不能使用。在这个研究项目中，我开发了一种新的统计方法来估计DNA多态的数量，即使在不同位置的选择限制不同的情况下也可以使用。我还得到了一种新的统计方法来从AFLP数据中估计DNA多态的数量。当自然选择在特定的地点进行时，我们不能使用中性理论。我曾经研究过自然选择对DNA多态的数量和模式的影响。一个有趣的结果是，即使自然选择在特定的地点进行，我们仍然可以用4Nv来估计DNA多态的数量，其中N是有效的种群大小，v是突变率。此外，我们还可以估计从种群中采样的DNA序列的祖先DNA序列。我还研究了种群结构对DNA多态数量的影响。

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.