Images Of Evolution: DNA Leaves Fossils In The Dust

The findings show that one human chromosome, Chromosome 7, is shared in its modern form only with chimpanzees, while human Chromosomes 16 and 19 have a more ancient evolutionary origin. Information from this study advances efforts to reconstruct evolutionary relationships between primates and between other mammalian species.

To track the history of a particular human chromosome, Florence Richard and colleagues looked for analogous chromosomes or chromosome fragments in other mammalian species. The researchers recognized these analogous fragments by tagging them with fluorescent molecules. They applied the tags to chromosomes from the Chinese tree shrew, nine-banded armadillo, mountain zebra, Diana monkey, and other representative species arising from the 130 million-year history of placental mammals.

By examining the regions of these animals' chromosomes that became brightly fluorescent, Richard and colleagues found, for example, that human chromosome 7 historically exists as two separate pieces in most non-primate mammals. They were able to determine how these pieces eventually migrated and fused together to form the present-day human chromosome 7. Applying this analysis to more chromosomes and species will help scientists not only to determine the origins of human chromosomes but also to reconstruct how our numerous mammalian relatives evolved from their ancient origins.