In a study published in the Oct. 20 issue of the journal Nature, Cornell scientists analyzed 11,624 genes, comparing how genes vary not only among 39 humans but also between the humans and a chimpanzee, whose DNA is 99 percent identical to humans.

The comparisons within and between species suggest that about 9 percent of genes that show some variability within humans or differences between humans and chimpanzees have evolved too rapidly to be explained simply by chance. The study suggests that positive Darwinian natural selection -- in which some forms of a gene are favored because they increase the probability of survival or reproduction -- is responsible for the increased rate of evolution. Since genes are blueprints for proteins, positive selection causes changes in the amino acid sequence of the protein for which the gene codes.

"Our study suggests that natural selection has played an important role in patterning the human genome," said the paper's lead author, Carlos Bustamante, assistant professor of biological statistics and computational biology at Cornell.

The Cornell/Celera team found that genes involved in immune function, sperm and egg production, sensory perception and transcription factors (proteins that control which genes are turned on or off) have been particularly affected by positive selection and show rapid evolution in the last 5 million years, when humans shared a common ancestor with chimps.

Likewise, the researchers found that approximately 13 percent of the genes that may vary show evidence of slightly deleterious or harmful mutations in human populations; these include genes involved in determining the basic structure of cells
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Contact: Krishna Ramanujan
ksr32@cornell.edu
607-255-3290
Cornell University News Service
21-Oct-2005