Genomic diversity between and within species reflects factors having affected evolution of the organisms in the past. Population genetics analyzes the present status of genetics diversity and makes inferences on the roles of those factors such as mutation, selection and population structure. In this paper, I summarize our recent studies using population genetic approaches. In the first part, a theoretical study on a nearly neutral mutation model is explained. It was shown that even very weak selection could be detected by analyzing DNA data from individuals carefully collected in multiple species. In the second part, preliminary results of a study on the molecular evolution of Cupressaceae, a group of conifer trees, is explained. Based on analyses of nonsynonymous and synonymous substitution rates, a stronger role played by mutation than by selection was suggested. Thus, somewhat different evolution seemed to have occurred in this species groups compared to those in other organisms thus far studied. Possible reasons for such differences are discussed paying attentions to their life characteristics.
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