Unformatted text preview: as that for the entire control region, because the former does not include a large segment of apparently invariable sites. For example, Wakeley (submitted) obtained a = 0.47 for the 250-bp 5’ -side hypervariable segment. This value is higher than the value for the entire control region, because the invariable segment is not included. The estimate of a is subject to sampling errors, and theoretically these errors are expected to affect the estimate of d. In practice, however, the effect of these errors is confounded with that of the sampling errors of PI, pz, and d, so that it is difficult to evaluate the effect. In the present case, our estimate of the age of the common ancestral mtDNA in humans was virtually the same as that obtained by Nei ( 1992) without using information on a. Furthermore, the $/a ratio, which is a function of a, was nearly the same for the human-chimpanzee comparison and for the human sequence comparison. These observations suggest that our estimation of a is reliable. Computer Program A computer request. Acknowledgments We would like to thank Mark Stoneking for providing DNA sequence data and John Wakeley for sending an unpublished manuscript. This work was supported by research grants, from the National Institute of Health and the National Science Foundation, to M.N.
ANDERSON, DROUIN, SMITH, program for computing d, S: 2, and their variances is available on CITED
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