dna fingerprinting

John MacFarlane jmacfarl at hgmp.mrc.ac.uk
Thu Oct 31 06:12:10 EST 1996


On Wed, 30 Oct 1996, V J Street wrote:

> I am in my third year at Sheffield University and am carrying out my 
> dissertation on the validity of DNA fingerprinting.  I know that the new 
> NRC report came out in May of this year, but can't find much information 
> on it.  If anybody can help me out I would be very grateful.

Dear Vicky,

Sorry no answer to your question but I'm going to rant on for a bit about
something unrelated! :)

I can remember many many moons ago also having to write an essay on
DNA fingerprinting. In an effort to get a new angle on what I was writing
about I contacted the Professor of criminal law at Edinburgh University.
What he had to say was quite eye opening. 

Old style fingerprinting involves matching a minimum of 12 reference
points between a suspects finger and a latent print. There is "no known
case of unrelated prints sharing 12 reference points". Pretty good stats
BUT to his knowledge no-one had ever been convicted on the strength of a
fingerprint alone.

When I gave him a ridiculously low figure of a DNA match being created by
chance 1 in 10 000 times he said that he would be quite happy to present
such a statistic to a jury because he was sure that he wouldn't be
prosecuting a case unless he had other evidence.

When DNA fingerprinting was first used the estimates of chance matches was
put in the range of 1 in several million. There then followed a perfectly
rational debate between scientists about the importance of which loci to
use, the importance of matching a suspect to the correct reference
population and what the actual figure for a chance match was. What
happened in the courts however was that lawyers jumped on the lack of
consensus and used this debate to baffle juries.

Now this is where I get on my soapbox...DNA fingerprinting is a classic
case of a scientific theory being unleashed on an un-ready public. 
Prosecutors immediately thought thay had a wonder method of banging up the
bad guys; defence lawyers dragged up scientists (even that idiot Keri
Mullis wanted to testify at the OJ trial) who got into a highly technical
debate that undermined the DNA evidence.

I'm not blaming either party outright but as a scientist I think that it's
time that we took a lot more responsibility for the effects of our work. 
Advances like gene therapy and the genome project are going to have huge
impact on the population of the world. Scientists alone should not make
decisions on how these technologies are used but neither should we simply
hand over policy making to the Governments and other legislative bodies. 

Not everyone is going to get a chance to sit on the big decision making
groups but it seems to me that bodies such as the MRC and the NIH could do
a lot more to get the people that they fund involved in Public
Understanding of Science programmes.

John MacFarlane




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