Within this 700 Kb region of human chromosome 2, the researchers identified segments of DNA that originated from 14 ancestral loci. These DNA segments, or "duplicons," ranged from 4-77 Kb in length and exhibited 94-99% sequence identity to their euchromatic predecessors.
The scientists then performed a comparative analysis of these duplicons in other primate species, including chimpanzee, gorilla, orangutan, baboon, and macaque. This analysis revealed that the duplicative transposition events leading to the establishment of these duplicons within the pericentromeric region occurred during a relatively narrow window of evolutionary time between 10-20 million years ago. This corresponds to the time period following the divergence of humans and Old World monkeys, but before the divergence of humans and great apes. For the past 10 million years, however, no such "duplicative seeding" events appear to have occurred in this region of the genome.
"It is unclear why pericentromeric seeding events have occurred so frequently during this period of human/great-ape evolutionary history," says Eichler. "It is also unclear as to why they suddenly cease, at least in the case of this pericentromeric region of chromosome 2."
Clearly, factors other than DNA sequence are necessary for such "punctuated" duplicative transposition events to occur during genome evolution. During the divergence of the human/great-ape lineage from the Old World monkey lineage, the genome may have been particularly permissive to segmental duplication events. The scientists speculate that the molecular driving forc
Source:Cold Spring Harbor Laboratory