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Image: By Aaron Logan, from http://www.lightmatter.net/gallery/albums.php
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CHIMP GENE GAP GROWS:
Using a new measure of genetic similarity--the number of copies of
genes that two species have in common--researchers report that chimps
and humans share only 94 percent of their genes, not the 98 to 99
percent frequently cited. |
A lot more genes may separate humans from their chimp
relatives than earlier studies let on. Researchers studying changes in
the number of copies of genes in the two species found that their mix
of genes is only 94 percent identical. The 6 percent difference is
considerably larger than the commonly cited figure of 1.5 percent.
The new finding supports the idea that evolution may have given
humans new genes with new functions that don't exist in chimps,
something researchers had not recognized until recently. The older
value of 1.5 percent is a measure of the difference between equivalent
genes in humans and chimps, like a difference in the spelling of the
same word in two similar languages. Based on that figure, experts
proposed that humans and chimps have essentially the same genes, but
differed in when and where the genes turn on and off. |
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| The new research takes
into account the possibility for multiple copies of genes and that the
number of copies can differ between species, even though the gene
itself is the same or nearly so. "You have to pay attention to more
than just the genes that are shared," says geneticist Matthew Hahn of
Indiana University, Bloomington, lead author of the new report.
Researchers believe that additional copies of the same gene allow
evolution to experiment, so to speak, finding new functions for old
genes.
Hahn and his colleagues set out to study these gains and losses in
gene number over the millennia by examining the genomes of humans,
chimps, mice, rats and dogs. They looked at 110,000 genes that fall
into 9,990 different families of similar genes.
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| The size of a gene family differed between species
in 5,622 cases, or 56 percent of all the families. These size changes
are so frequent in the evolutionary history of mammals that genes might
as well be going through a revolving door, the researchers write in a
paper published in a new online journal, PLoS ONE.
In humans and chimps, which have about 22,000 genes each, the group
found 1,418 duplicates that one or the other does not possess. For
example, humans have 15 members of a family of brain genes linked to
autism, called the centaurin-gamma family, whereas chimps have six, for
a difference of nine gene copies.
The group estimated that humans have acquired 689 new gene
duplicates and lost 86 since diverging from our common ancestor with
chimps six million years ago. Similarly, they reckoned that chimps have
lost 729 gene copies that humans still have.
"The paper supports the emerging view that change in gene copy
number, via gene duplication or loss, is one of the key mechanisms
driving mammalian evolution," says genomics researcher James Sikela of
the University of Colorado Health Sciences Center. |
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RELATED LINKS:
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Scientists Identify Gene Difference Between Humans and Chimps
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Chimp Genome--and First Fossils--Unveiled
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What does the fact that we share 95 percent of our genes with the chimpanzee mean?
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Genetic Activity Marks Difference between Brains of Humans and Chimps
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