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October 25, 2011
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“Junk DNA” may help explain human-chimp differences
Oct. 25, 2011
Courtesy of Georgia Tech
and World
Science staff
For years, scientists thought an explanation would soon turn up for the vast differences between humans and their closest relatives among the animals, such as chimpanzees. The difference must be in the genes, biologists reasoned. Researchers say a major part of the
explanation for human-chimp differences lies in regions of DNA outside those traditionally considered genes.
(Image courtesy of Georgia Tech)
But this hypothesis ran into trouble when it later emerged that human and chimp genes are nearly identical. So what’s going on?
Researchers at the Georgia Institute of Technology have now concluded that a major part of the answer lies in regions of DNA outside those
that are considered genes. This material was called junk DNA only a few years ago because it had no discernible function:
unlike genes it doesn’t provide code for producing proteins, the myriad molecules that do much of the day-to-day work of keeping the organism ticking.
But much “junk DNA,” now more often called non-coding DNA, does have an impact on how hard regular genes work, as well as where and when they do so. That function, more than the gene sequences themselves, may account for many of the key differences between us and our evolutionary relatives, the biologists are now proposing.
“Our findings are generally consistent with the notion that the morphological [physical] 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 Georgia Tech biologist John McDonald, who led the new research.
His team examined a major type of non-coding DNA called retrotransposons, which comprise
about half of the genomes of both humans and chimps. Retrotransposons, also called transposable elements, are strips of DNA that over evolutionary history insert themselves into and delete themselves from various places in our the larger DNA structure—a behavior not unlike that of certain viruses.
Retrotransposons near genes are highly variable between humans and chimps and may account for major differences between the two species, McDonald asserts. The team’s findings are reported in the current issue of the research journal
Mobile DNA. “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 said.
The research team examined retrotransposon-rich areas between genes, known as genomic gaps, in both species and found that they’re significantly correlated with differences in gene activity reported previously by researchers at the Max Plank Institute for Evolutionary Anthropology in Germany.
The Georgia Tech researchers also said their own project was motivated by a 2009 study of theirs finding that people’s higher cancer rates relative to chimps may have been a byproduct of evolutionary pressure for larger brains.
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For years, scientists thought an explanation would soon turn up for the vast differences between humans and their closest relatives among the animals, such as chimpanzees. The difference must be in the genes, biologists reasoned. But this hypothesis ran into trouble when it later emerged that human and chimp genes are nearly identical. So what’s going on? Researchers at the Georgia Institute of Technology have now concluded that a major part of the answer lies in regions of DNA outside those traditionally considered genes. This material was called junk DNA only a few years ago because it had no discernible function: it doesn’t provide code for producing proteins, the myriad molecules that do much of the day-to-day work of keeping the organism ticking. But much “junk DNA,” now more often called non-coding DNA, does have an impact on how hard regular genes work, as well as where and when they do so. That function, more than the gene sequences themselves, may account for many of the key differences between us and our evolutionary relatives, the biologists are now proposing. “Our findings are generally consistent with the notion that the morphological [physical] 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 Georgia Tech biologist John McDonald, who led the new research. His team examined a major type of non-coding DNA called retrotransposons, which comprises about half of the genomes of both humans and chimps. Retrotransposons, also called transposable elements, are strips of DNA that over evolutionary history insert themselves into and delete themselves from various places in our the larger DNA structure—a behavior not unlike that of certain viruses. Retrotransposons near genes are highly variable between humans and chimps and may account for major differences between the two species, McDonald asserts. The team’s findings are reported in the current issue of the research journal Mobile DNA. “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 said. The research team examined retrotransposon-rich areas between genes, known as genomic gaps, in both species and found that they’re significantly correlated with differences in gene activity reported previously by researchers at the Max Plank Institute for Evolutionary Anthropology in Germany. The Georgia Tech researchers also said their own project was motivated by a 2009 study of theirs finding that people’s higher cancer rates relative to chimps may have been a byproduct of evolutionary pressure for larger brains in us.