Population growth of human Y chromosomes: A study of Y chromosome microsatellites

We use variation at a set of eight human Y chromosome microsatellite loci t o investigate the demographic history of the Y chromosome. instead of assum ing a population of constant size, as in most of the previous work on the Y chromosome, we consider a model which permits a period of recent populatio n growth. We show that for most of the populations in our sample this model fits the data far better than a model with no growth. We estimate the demo graphic parameters of this model for each population and also the time to t he most recent common ancestor. Since there is some uncertainty about the d etails of the microsatellite mutation process, we consider several plausibl e mutation schemes and estimate the variance in mutation size simultaneousl y with the demographic parameters of interest. Our finding of a recent comm on ancestor (probably in the last 120,000 years), coupled with a strong sig nal of demographic expansion in all populations, suggests either a recent h uman expansion from a small ancestral population, or natural selection acti ng on the Y chromosome.