Conservation of pericentromeric duplications of a 200-kb part of the human 21q22.1 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 regions of chromosomes 2, 13, and 18 in three nonhuman primate species. Orthologous regions were found by FISH analysis of metaphase chromosomes from Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus. Only one orthologous region was detected in chromosomes of P. pygmaeus, showing that the original locus was at 21q22.1 and that the duplication arose after the separation of Asian orangutans from the other hominoids. Surprisingly, the paralogous regions were more highly conserved in gorilla than in chimpanzee. PCR amplification of STSs derived from sequences of the chromosome 21 loci and low-stringency FISH analysis showed that this duplication occurred recently in the evolution of the genome. Different rates of sequence evolution through substitutions or deletions, after the duplication, may have resulted in diversity between closely related primates.