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http://www.sciencedaily.com/releases/2008/08/
080813144407.htm
How DNA Repairs Can Reshape Genome, Spawn New Species
enlarge
Researchers
have shown how broken sections of chromosomes can recombine to change
genomes and spawn new species. (Credit: iStockphoto/Andrey Volodin)
ScienceDaily (Aug. 14, 2008) — Researchers at Duke University Medical Center
and at the National
Institute of Environmental Health Sciences (NIEHS) have shown how
broken sections of chromosomes can recombine to change genomes and
spawn new species.
"People have discovered high levels of repeated sequences in the
genomes of most higher species and spun theories about why there are so
many repeats," said Lucas Argueso, Ph.D., a research scholar in Duke's
Department of Molecular Genetics and Microbiology. "We have been able
to show with yeast that these repeated sequences allow the formation of
new types of chromosomes (chromosome aberrations), and represent one
important way of diversifying the genome."
The scientists used X-rays to break yeast chromosomes, and then
studied how the damage was repaired. Most of the chromosome aberrations
they identified resulted from interactions between repeated DNA
sequences located on different chromosomes rather than from a simple
re-joining of the broken ends on the same chromosome.
Chromosome aberrations are a change in the normal chromosome
complement because of deletion, duplication, or rearrangement of
genetic material. On rare occasions, the development of one of these
new chromosome structures is beneficial, but more often DNA changes can
be detrimental, leading to problems like tumors.
"Every so often the rearrangements may be advantageous," Argueso
said. "Those particular differences may prove to be more successful in
natural selection and eventually you may get a new species."
The radiation-induced aberrations in yeast were initially detected
by co-author Jim Westmoreland in the NIEHS Laboratory of Molecular
Genetics and the molecular dissection was done by Duke's Argueso.
In the yeast used for this study, the repeated DNA sequences account
for about 3 percent of the genome. In higher species, like humans,
about half of the genome consists of these repeated sequences, "which
makes for an Achilles heel among humans," Argueso said. "If you have a
break in this repeated part, you can repair not only from the same
chromosome, but also from a similar repeated sequence in many other
places in the genome."
Sequencing the genomes of different humans has turned up a
surprising amount of structural variation between individuals, said
Thomas D. Petes, Ph.D., chair of Duke molecular genetics and
microbiology and co-author of the yeast study. "We expected to see
primarily single base pair changes or small deletions and insertions.
No one expected to see that one person would have two copies of a gene,
while others would have one or three copies of the same gene."
These human studies also showed that many of the rearrangements
found in humans are at sites of repeated DNA, which may occur through a
mechanism similar to what this study found in yeast.
Petes said this work with yeast also could prove relevant to cancer
research. "Most solid tumors have a high level of these rearrangements,
as well as a high level of extra chromosomes; recombination between
repeated genes is clearly one way of generating rearrangements,
although some rearrangements also occur by other pathways," he said.
"It is an evolutionary battle between normal cells and tumor cells. One
way that tumor cells can break free of normal cell growth regulation is
to rearrange their genomes."
The study was to be published online August 13 in the Proceedings of
the National Academy of Sciences in collaboration with senior author
Michael A. Resnick of the Laboratory of Molecular Genetics at NIEHS.
Funding for this study came from a National Institutes of Health grant
and by intramural research funds from the National Institute of
Environmental Health Sciences. Other authors on the paper were Piotr A.
Mieczkowski and Malgorzata Gawel of the Duke Department of Molecular
Genetics and Microbiology.
________________________________
Adapted from materials provided by Duke University Medical Center.
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Duke University Medical Center (2008, August 14). How DNA Repairs Can Reshape
Genome, Spawn New Species. ScienceDaily. Retrieved August 14, 2008, from
http://www.sciencedaily.com/releases/2008/08/080813144407.htm
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