ALU FOSSIL RELICS - DISTRIBUTION AND INSERTION POLYMORPHISM

Screening of a human genomic library with an oligonucleotide probe spe cific for one of the young subfamilies of Alu repeats (Ya5/8) resulted in the identification of several hundred positive clones. Thirty-thre e of these clones were analyzed in detail by DNA sequencing. Oligonucl eotide primers complementary to the unique sequence regions flanking e ach Alu repeat were used in PCR-based assays to perform phylogenetic a nalyses, chromosomal localization, and insertion polymorphism analysts within different human population groups. All 33 Alu repeats were pre sent only in humans and absent from orthologous positions in several n onhuman primate genomes. Seven Alu repeats were polymorphic for their presence/absence in three different human population groups, making th em novel identical-by-descent markers for the analysis of human geneti c diversity and evolution. Nucleotide sequence analysis of the polymor phic Alu repeats showed an extremely low nucleotide diversity compared with the subfamily consensus sequence with an average age of 1.63 mil lion years old. The young Alu insertions do not appear to accumulate p referentially on any individual human chromosome.