Monday, January 11, 2010

New techniques for sequencing

I mentioned that genetic sequencing is now one of the important tools used in systematics. However up until now this has been problematic when working with early human specimens, or close relatives. This is because the technique involved multiplying up small fragments of DNA and so even a tiny amount of contamination from a modern human (eg an archaeologist who handled the bones) could become a huge problem if this contaminant were multiplied.

'Using the remains of humans that lived in Russia about 30,000 years ago, Svante Pääbo and his colleagues now make use of the latest DNA sequencing (i.e., reading the sequence of bases that make up the DNA strands) techniques to overcome this problem. These techniques, known as "second-generation sequencing," enable the researchers to "read" directly from ancient DNA molecules, without having to use probes to multiply the DNA. Moreover, they can read from very short sequence fragments that are typical of DNA ancient remains because over time the DNA strands tend to break up. By contrast, DNA that is younger and only recently came in contact with the sample would consist of much longer fragments. This and other features, such as the chemical damage incurred by ancient as opposed to modern DNA, effectively enabled the researchers to distinguish between genuine ancient DNA molecules and modern contamination. "We can now do what I thought was impossible just a year ago -- determine reliable DNA sequences from modern humans -- but this is still possible only from very well-preserved specimens," says Pääbo.'

The paper is in the Jan 12 edition of Current Biology and there's a more popular write up on the ScienceDaily website.

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