Conservation of pericentromeric duplications of a 200-kb part of the human21q22.1 region in primates

We analyzed the conservation of large paralogous regions (more than 200 kb) on human chromosome regions 21q22.1 and 21q11.2 and on pericentromeric reg ions of chromosomes 2, 13, and 18 in three nonhuman primate species. Orthol ogous regions were found by FISH analysis of metaphase chromosomes from Gor illa gorilla, Pan troglodytes, and Pongo pygmaeus. Only one orthologous reg ion was detected in chromosomes of P.pygmaeus, showing that the original lo cus was at 21q22.1 and that the duplication arose after the separation of A sian orangutans from the other hominoids. Surprisingly, the paralogous regi ons were more highly conserved in gorilla than in chimpanzee. PCR amplifica tion of STSs derived from sequences of the chromosome 21 loci and low-strin gency FISH analysis showed that this duplication occurred recently in the e volution of the genome. Different rates of sequence evolution through subst itutions or deletions, after the duplication, may have resulted in diversit y between closely related primates.