Ice Age park? Scientists sequence mammoth genomeNovember 20th, 2008 - 1:54 pm ICT by IANS
Washington, Nov 20 (IANS) Scientists have sequenced the genome of the woolly mammoth of the Ice Age, bringing to reality the possibility of an Ice Age park in the lines of the fictional Jurassic Park of Michael Crichton.With four billlion DNA bases, the sequencing has been done for the first time, using new generation tools and a novel technique that reads the DNA bases far more efficiently.
Mammoths roamed the northern hemisphere during the last Ice Age.
“Previous studies on extinct organisms have generated only small amounts of data,” said Stephan C. Schuster, professor of biochemistry and molecular biology at Penn State University and the project leader with Webb Miller, Penn professor of biology and computer science.
“Our dataset is 100 times more extensive than any other published dataset for an extinct species, demonstrating that ancient DNA studies can be brought up to the same level as modern genome projects,” added.
The team sequenced the mammoth’s nuclear genome using DNA extracted from the hairs of a mammoth mummy that had been buried in the Siberian permafrost for 20,000 years and a second mammoth mummy that is at least 60,000 years old.
By using hair, the scientists avoided problems that have bedeviled the sequencing of ancient DNA from bones because DNA from bacteria and fungi, which always are associated with ancient DNA, can more easily be removed from hair than from bones.
Another advantage of using hair is that less damage occurs to ancient DNA in hair because the hair shaft encases the remnant DNA like a biological plastic, thus protecting it from degradation and exposure to the elements.
Although their data set consists of more than four-billion DNA bases, only 3.3 billion of them - a little over the size of the human genome - currently can be assigned to the mammoth genome.
Some of the remaining DNA bases may belong to the mammoth, but others could belong to other organisms, like bacteria and fungi, from the surrounding environment that had contaminated the sample.
The team used a draft version of the African elephant’s genome, which currently is being generated by scientists at the Broad Institute of MIT and Harvard, to distinguish those sequences that truly belong to the mammoth from possible contaminants.
“Only after the genome of the African elephant has been completed will we be able to make a final assessment about how much of the full woolly-mammoth genome we have sequenced,” said Miller. The team plans to finish sequencing the woolly mammoth’s genome when the project receives additional funding.
The researchers previously had sequenced the woolly mammoth’s entire mitochondrial genome, which codes for only 13 of the mammoth’s roughly 20,000 genes but is relatively easy to sequence because each of the mammoth’s cells has many copies.
In their most recent project, the team sequenced the mammoth’s nuclear genome, which codes for all the genetic factors that are responsible for the appearance of an organism, said a Penn State release.
The two methods combined have yielded information about the evolution of the three known elephant species: the modern-day African and Indian elephants and the woolly mammoth.
The team found that woolly mammoths separated into two groups around two million years ago, and that these groups eventually became genetically distinct sub-populations.
“Our data suggest that mammoths and modern-day elephants separated around six-million years ago, about the same time that humans and chimpanzees separated,” said Miller.
“However, unlike humans and chimpanzees, which relatively rapidly evolved into two distinct species, mammoths and elephants evolved at a more gradual pace,” added Schuster, who believes that the data will help to shed light on the rate at which mammalian genomes, in general, can evolve.