Monday, May 16, 2005

1 percent genetic difference with chimps made humans cancer prone

Distribution of Mutations: The figure shows the number of synonymous, antonymous, and nonsynonymous nucleotide differences in 13,731 human--chimpanzee orthologous gene pairs. From: Nielsen R, Bustamante C, Clark AG, Glanowski S, Sackton TB, et al. (2005) A Scan for Positively Selected Genes in the Genomes of Humans and Chimpanzees. PLoS Biol 3(6): e170

Chimpanzees and humans share a common ancestor, and even today 99 percent of the two species' DNA is identical. But since the paths of man and chimp diverged 5 million years ago, that one percent of genetic difference appears to have changed humans in an unexpected way: It could have made people more prone to cancer.

A comparative genetic study led by Cornell University researchers suggest that some mutations in human sperm cells might allow them to avoid early death and reproduce, creating an advantage that ensures more sperm cells carry this trait. But this same positive selection could also have made it easier for human cancer cells to survive.

"If we are right about this, it may help explain the high prevalence of cancer," says Rasmus Nielsen, lead author of the paper, and a former assistant professor of the Department of Biological Statistics and Computational Biology at Cornell who is now a professor at the University of Copenhagen, Denmark. The study, published in a recent issue of PLoS Biology (Vol. 3, Issue 6), a peer-reviewed, open-access journal published by the Public Library of Science (PLoS), focuses on identifying biological processes where positive selection -- adaptations that lead to new directions -- produced evolutionary changes that can be identified in the genomes of both humans and chimps.


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