Differential Alu mobilization and polymorphism among the human and chimpanzee lineages

Alu elements are primate-specific members of the SINE (short interspersed element) retroposon family, which comprise -10% of the human genome. Here we report the first chromosomal-level comparison examining the Alu retroposition dynamics following the divergence of humans and chimpanzees. We find a twofold increase in Alu insertions in humans in comparison to the common chimpanzee (Pan troglodytes). The genomic diversity (polymorphism for presence or absence of the Alu insertion) associated with these inserts indicates that, analogous to recent nucleotide diversity studies, the level of chimpanzee Alu diversity is -1.7 times higher than that of humans. Evolutionarily recent Alu subfamily structure differs markedly between the human and chimpanzee lineages, with the major human subfamilies remaining largely inactive in the chimpanzee lineage. We propose a population-based model to account for the observed fluctuation in Alu retroposition rates across primate taxa.