In the news: Cornell finds natural selection in humans
- From: John Wilkins <john@xxxxxxxxxxxxx>
- Date: Sat, 22 Oct 2005 16:44:37 +1000
http://www.eurekalert.org/pub_releases/2005-10/cuns-cfn102105.php
ITHACA, N.Y. -- The most detailed analysis to date of how humans differ from
one another at the DNA level shows strong evidence that natural selection has
shaped the recent evolution of our species, according to researchers from
Cornell University, Celera Genomics and Celera Diagnostics.
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 and muscles as well as genes that control traffic in and
out of the cell. These mutations are subject to weak negative selection,
according to the study. In general, negative selection eliminates from the
population very harmful changes to proteins that kill or stop reproduction.
But mutations that have led to slightly deleterious versions of the gene --
mutations that may cause disease or only slightly reduce the average number of
children left by those that carried the mutation -- can by chance become quite
common in the population.
The authors also found a correlation between genes predicted to be under
negative selection and genes implicated in certain hereditary diseases. For
example, among the genes the researchers predicted to be under negative
selection are those involved in muscular dystrophy and in Usher syndrome, the
most common cause of congenital blindness and deafness in developed countries.
"We have a long way to go before we can predict from looking at sequences,
which mutations in which genes and under which environmental conditions can
ultimately lead to disease. This is a first step in identifying the classes of
genes that appear to be particularly vulnerable to these types of changes,"
said Bustamante.
A team from Celera initiated the project and sequenced more than 20,000 genes
in 39 humans and a chimpanzee. By comparing the DNA sequences of the 39 human
subjects across the 20,000 genes, the Celera researchers identified DNA sites
in the genome where individuals in the sample differed from one another. The
chimpanzee sequence was then used to identify which form of the gene was the
original ancestral form and which was the derived or new type. The original
goal of the project was to identify novel amino acid variants that could then
be tested for association with human disease in subsequent studies. The
Cornell researchers became involved at the analysis stage in order to make
predictions about what types of changes are most likely to be functionally
important.
[For Larry Moran ;-)]
--
John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project
University of Queensland - Blog: evolvethought.blogspot.com
"Darwin's theory has no more to do with philosophy than any other
hypothesis in natural science." Tractatus 4.1122
.
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