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.
Characterization and potential functional significance of human-chimpanzee large INDEL variation
