Two tetranucleotide repeats within the Xq21.3/Yp11.2 human specific regionof homology and their conservation in primate evolution

We locate two tetranucleotide repeat sequences (AT3 and T2C2) between the m arkers sY44 and sY46 within the Xq21.3/Yp block of homology that has been c reated since the separation of the chimpanzee and human lineages, and trace their origin in primate evolution. The T2C2 repeat is present only in homi noid primates. The sequence AT3 is present in Old World monkeys but not in New World monkeys, and has been lost in some gibbon species. in the bonobo, the AT3 repeat is the site of a new Alu insertion. These findings and thei r relationship to the conservation of other markers in this region cast lig ht on the structure of a genomic region that has been subject to change in the course of primate evolution and may include one or more sites of instab ility.