ALU EVOLUTION IN HUMAN-POPULATIONS - USING THE COALESCENT TO ESTIMATEEFFECTIVE POPULATION-SIZE

There are estimated to be similar to 1000 members of the Ya5 Alu subfa mily of retroposons in humans. This subfamily has a distribution restr icted to humans, with a few copies in gorillas and chimpanzees. Fifty- seven Ya5 elements were previously cloned from a HeLa-derived randomly sheared total genomic library, sequenced, and screened for polymorphi sm in a panel of 120 unrelated humans. Forty-four of the 57 cloned Alu repeats were monomorphic in the sample and 13 Alu repeats were dimorp hic for insertion presence/absence. The observed distribution of sampl e frequencies of the 13 dimorphic elements is consistent with the theo retical expectation for elements ascertained in a single diploid cell line. Coalescence theory is used to compute expected total pedigree br anch lengths for monomorphic and dimorphic elements, leading to an est imate of human effective population size of similar to 18,000 during t he last one to two million years.