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DNA evidence is bone of contention

world Updated: Feb 05, 2013 23:18 IST
Alok Jha
Alok Jha
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The DNA evidence was, apparently, the killer piece of evidence in the puzzle of the twisted skeleton under the car park in Leicester.

A team of scientists led by Turi King at the University of Leicester’s eminent genetics department had conclusively proved these were the remains of King Richard III.

Given that the DNA analysis seems to corroborate other genealogical evidence, the conclusion seems clear-cut. But no genetic analysis is perfect.

King’s team looked at the DNA from the mitochondria of the cells in the skeleton — these tiny structures are a cell’s batteries, turning glucose into power for all of its functions.

Crucially for genealogists, this DNA sequence is separate from a person’s main sequence and is passed down the maternal line almost unchanged across many generations.

Comparing the so-called “mtDNA” from the skeleton with that from a living descendant, Michael Ibsen, showed a match, meaning Ibsen’s mother and the skeleton’s mother are likely to have shared a lineage.

“Mitochondria is not brilliant for detecting relatedness but, given you’ve got so far back in time, so many generations back, it’s as good as it can get. If the only thing you can compare that ancient DNA with is somebody living today, then you’d want it to be mitochondria,” said Mark Thomas, a professor of evolutionary genetics at University College London.

But it is not ideal. Two people could have the same mitochondrial type just by chance and it would not necessarily mean they shared a common ancestor at the time of Richard III.

“If Richard III had a very common type of mitochondrial DNA, then there will be plenty of people in the country that have got the same,” said Thomas.

Even if there is good circumstantial evidence to suggest two people are related, they might still share the same mtDNA by chance.

One thing to look out for in any forthcoming research paper is just how rare the mtDNA type is that King’s team measured — the rarer it is, the less likely it is to be a chance result and the more likely it is to be a robust family connection.

Ross Barnett of the Centre for GeoGenetics at the Natural History Museum in Copenhagen also questioned the depth of the mtDNA match between the skeleton and Ibsen.

“The [diagrams] they showed were only about 30 base pairs or so … you need to have quite a lot more than 30 base pairs to get a deep match.” The more common a mtDNA type is in the population, the more base pairs of DNA are required to get a reliable match.

Thomas said in this instance the DNA is of less importance in determining the identity.

“People tend to privilege DNA because they see it as firm science [but only when] you put it together with the spine deformation, the wounds and so on, it makes for a more persuasive case.” GNS

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