A statistical test for the difference in the amounts of DNA variation between two populations

A statistical test for the difference in the amounts of DNA variation between two populations is developed. The test statistic involves the covariance of the amount of variation between two populations, which is given by a function of their divergence time, T-0. Accordingly, the power (rejection probability) of the test depends on T-0. In this article, T-0 is treated as unknown because it is very difficult to estimate. The test is most conservative when T-0 = infinity is assumed because the covariance is zero. If T-0 = 0 is assumed, the largest value of the rejection probability is obtained. Thus, the test provides a range of rejection probability unless we have a reliable estimate of T-0. The test is applied to the PgiC region in three mustard species: Leavenworthia stylosa, L. crassa and L. uniflora. The results of our test show that the level of variation in L. stylosa is significantly higher than those in the other species.