Is DNA testing reliable?

wijsman at max.u.washington.edu wijsman at max.u.washington.edu
Thu Oct 27 17:02:05 EST 1994


>: I have a friend (no not me thank God) who is being sued by a woman
>: for maintenance for a kid  she says was fathered by my friend.
>: He swears it's not his and wants to avoid the cost and stigma
>: (he was just married) of a court case.  I recommended he get a DNA
>: test done, but I know nothing about it.  What I'm wondering is if
>: anyone can tell me a) the reliability of these tests, especially
>: in the eyes of the courts and b) the cost and availibility of these
>: tests in the Victoria or Vancouver BC Canada area.  I seem to remember
>: reading that the test costs about $400 and it can be done in
>: Vancouver but I'm not certain of this.  If someone could please
>: answer these questions I would greatly appreciate it.  Thanx.
>:

Yes, DNA testing is reliable, and quite accepted by the courts.  For true
non-paternities the exclusion rate is extremely high (thus a
non-exclusionary result is usually considered to be pretty strong evidence
in favor of paternity).  I don't know about costs/availability in the
Vancouver BC Canada area, but there is  at least one company in the Seattle
area which does such tests.  I don't know what they cost.
  
>How about a simple blood test? It can exclude parentage. For example if 
>the mother is type A, the friend type O, and the child type B he has 
>nothing to worry about.  In this case the friend can pass on only the O 
>gene.  With a mother who is type A (A/A or A/O) only a type A (A/O) or 
>type O (O/O) can be created.  The Red Cross will type blood in return for 
>a pint.  If the blood typing doesn't exclude parentage, then it's time 
>for a more complex DNA test that a local lab should be able to do.
>Don't forget the eye colour test, if both parents have blue eyes and the 
>kid has brown eyes, one of the parents isn't.  Again this can only 
>exclude parentage.

A blood test can certainly be used for exclusion, but even in the case
where the accused is not the father, there is a very low probability of
exclusion for most blood-type markers.  Eye-color is NOT a good test. 
Most physical characteristics, including eye-color, have a complex enough
mode of inheritance that it isn't possible to easily quantify the evidence
for or against paternity.  The old blue-eye/brown-eye story which we are
fed in high school biology is not a correct description of eye-color
inheritance, and would probably not stand up in court.

Ellen Wijsman
Div of Medical Genetics, RG-25
and Dept of Biostatistics
University of Washington
Seattle, WA   98195
wijsman at u.washington.edu



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