A GENE TREE FOR BETA-GLOBIN SEQUENCES FROM MELANESIA

We have analyzed allelic sequence variation in sixty-one 3-kb beta-glo bin sequences from the Melanesian population of Vanuatu to demonstrate the value of (1) turning to the autosomal nuclear genome for studies on the evolution of modern humans and (2) using new analytical methods based on a coalescent model. After excluding recombination events, be ta-globin sequence variants were connected in a unique gene tree, A ge ne tree provides more information for inferences on the population gen ealogy than simple summary statistics such as the average pairwise seq uence difference. Estimates of the time to the most recent common ance stor (MRCA) and of the ages of each mutation, conditional on the gene tree, were made using new maximum Likelihood methods assuming a coales cent model. We found that allelic beta-globin variation coalesces to a single shared ancestral haplotype over a time scale of approximately 900,000 years. Three major haplotypes (A1, B1, C3) that are older than 200,000 years identify ancestral diversity contemporaneous with the s ingle MRCA for mitochondrial variation.