Sequence diversity and chromosomal distribution of "young" Alu repeats

Members of the recently inserted human-specific (HS)/predicted variant (PV) subfamily of Alu elements were sequenced. A number of these Alu elements share greater than 98% sequence identity with the subfamily consensus sequence, and they are flanked by perfect 5' and 3' direct repeats ranging in size from 6 to 15 nucleotides (nt). Based on the low number of random mutations, the estimated average age of these elements was calculated to be 1.5 million years (Myr). All the young Alu subfamily members were restricted to the human genome, as judged by polymerase chain reaction (PCR) amplification of human and non-human primate DNA samples using the unique flanking sequences specific for each Alu element. The chromosomal locations of several Alu elements belonging to the young subfamilies, designated as HS/PV and Sb2, were determined by PCR amplification of DNA samples from human/rodent somatic cell hybrid panels. A statistical analysis of the chromosomal distribution pattern showed that the recently inserted Alu elements appear to integrate randomly in the human genome.