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"Junk DNA" Defines Differences Between Humans and Chimps
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For years, scientists believed the vast phenotypic
differences between humans and chimpanzees would be easily explained – the two
species must have significantly different genetic makeups. However, when their
genomes were later sequenced, researchers were surprised to learn that the DNA
sequences of human and chimpanzee genes are nearly identical. What then is
responsible for the many morphological and behavioral differences between the
two species? Researchers at the Georgia Institute of Technology have now
determined that the insertion and deletion of large pieces of DNA near genes
are highly variable between humans and chimpanzees and may account for major
differences between the two species.
The research team lead by Georgia Tech Professor of Biology
John McDonald has verified that while the DNA sequence of genes between humans
and chimpanzees is nearly identical, there are large genomic “gaps” in areas adjacent
to genes that can affect the extent to which genes are “turned on” and “turned
off.” The research shows that these genomic “gaps” between the two species are predominantly
due to the insertion or deletion (INDEL) of viral-like sequences called
retrotransposons that are known to comprise about half of the genomes of both
species. The findings are reported in the most recent issue of the online,
open-access journal Mobile DNA.
“These genetic gaps have primarily been caused by the
activity of retroviral-like transposable element sequences,” said McDonald. “Transposable
elements were once considered ‘junk DNA’ with little or no function. Now it
appears that they may be one of the major reasons why we are so different from
chimpanzees.”
McDonald’s research team, comprised of graduate students Nalini
Polavarapu, Gaurav Arora and Vinay Mittal, examined the genomic gaps in both
species and determined that they are significantly correlated with differences
in gene expression reported previously by researchers at the Max Plank
Institute for Evolutionary Anthropology in Germany.
“Our findings are generally consistent with the notion that the
morphological and behavioral differences between humans and chimpanzees are
predominately due to differences in the regulation of genes rather than to
differences in the sequence of the genes themselves,” said McDonald.
The current analysis of the genetic differences between
humans and chimpanzees was motivated by the group’s previously published
findings (2009) that the higher propensity for cancer in humans vs. chimpanzees
may have been a by-product of selection for increased brain size in humans.
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- Workflow Status: Published
- Created By: Jason Maderer
- Created: 10/25/2011
- Modified By: Fletcher Moore
- Modified: 10/07/2016
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