DNA Fingerprinting - Simpson Trial

Harry Menegay hxm8 at po.cwru.edu
Sat Feb 25 17:11:23 EST 1995

szcooley at dale.ucdavis.edu (Michael Cooley) wrote:
> Janet Hays (BIO) (jhays at chuma.cas.usf.edu) wrote:

> : It is even possible through pipette aerosol contamination when 
> : putting the master mix (no template) into the various tubes with the 
> : template DNA. You mix a master for several samples, and then apportion it 
> : between them. If on putting part of the master into one sample, say NBS, 
> : and then put the next portion into the OJ tube, poor technique may allow 
> : carryover of the DNA in the first tube to the second tube. At this point 
> : the second tube will show as a having two genomes though it wasn't 
> : extracted as such. There are methods and equipment that can avoid this 
> : kind of error, and perhaps these labs use them, but I for one am 
> : unwilling to assume that they have.
> It is obvious that this JK person has not done much or any PCR. Any fool 
> knows you don't assemble the reactions in this manner. Furthermore 
> considering the pressure on these labs to do it right, I doubt seriously 
> that anything of the sort would happen.

No doubt!  Aerosol contamination?  Labs that do PCR and worry about 
contamination use filtered tips to prevent that.  It's a pretty basic
first level step.  We go way beyond that with UV hoods and a lot of
other safety precautions. And you DON'T assemble the reaction this way
anyway.  Real PCR people, as I assume they have at these labs, can
take a lot of measures to prevent contamination occuring in the lab.
After that you only have to worry about the person who originally
collected the samples being one of the 1 in 10,000 or better people 
who match the subject. Not very likely.

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