How DNA may tell police the surname of the criminal

["Gary Funck" <gary () intrepid com>]

How DNA may tell police the surname of the criminal
http://www.guardian.co.uk/crime/article/0,,1715022,00.html
Alok Jha
Wednesday February 22, 2006
The Guardian
Police will soon be able to predict the surnames of criminals whose DNA is
found at crime scenes, according to research published yesterday. The
technique would only work in finding men, however, as it is based on
identifying similarities in the Y chromosome, which is passed from father to
son.
The technique relies on research carried out by University of Leicester
scientists into how Y chromosomes have spread through the British
population. They analysed these chromosomes in 150 pairs of men with the
same surname and found that, in a quarter of cases, the pair had matching Y
chromosomes.
When the most common names were excluded from the list - Smith, Jones,
Williams and Taylor, for example - the chance that two men with the same
surname shared a Y chromosome jumped to 50%. The research appears in the
latest edition of Current Biology.
Mark Jobling, a geneticist at the University of Leicester who led the work,
said the police would need a relatively small collection of male DNA -
around 40,000 people - to allow useful matches to be made. "That sounds big
but the national DNA database is nearly 100 times bigger," he said. By
matching the Y chromosome details of unidentified DNA at a crime scene with
the database, police would get a list of potential surname matches.
"That would allow you to prioritise suspects in your investigation," said Dr
Jobling. "If you have a lot of suspects - say a whole town or something -
you can say we have 50 names, are these names represented here, if so let's
go and interview these people."
Y chromosomes are passed from father to son mostly unaltered. Once in a
while, they will acquire random mutations as they pass through the
generations. Some parts of the chromosome are known to mutate less rapidly
than others and, by mapping these differences, scientists can create a tree
showing the relationships between different Y chromosomes.
"If men fall in different branches of the tree, there's no way they can be
related to a recent male ancestor," said Dr Jobling. "If they lie within the
same branch, there is a chance they are, but it doesn't prove it.
"When we do that simple test, we find that a highly statistically
significant excess of pairs share a branch of the tree, much more than we
expect by chance."
It is a surprising result, since there are plenty of reasons why people
might have the same surname but be unrelated: many names were founded by
more than one man, for example. There is also the issue of illegitimacy. The
researchers predicted that more than 1% of children were illegitimate in
each generation. Over many generations, this could have built up a
significant error.
"Those two elements would act as a strong force to break any links," said Dr
Jobling. "It was a surprise that by choosing just pairs we got a clear
signal of sharing ancestors."



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