From: nkk@wet.UUCP (Butch Katigbak)
Newsgroups: sci.med
Subject: PATERNITY TEST SCIENTIFIC AND LEGAL INFORMATION
Date: 29 Jul 92 23:42:00 GMT


Subject: Info needed on DNA vs blood tests for paternity determination
Organization: University of Colorado, Boulder

I am involved in a paternity case in the Chicago area.  I would like
to know as soon as possible whether this child is mine.   (If it is,
my wife and I intend to pursue custody.)  I have heard of various blood 
tests and DNA tests.  Can the DNA tests be performed earlier than at six
months, as is the case for the blood tests?  Are these tests of the
same reliability?  What literature is there on these tests?

James Gearson
=========================================================

From a publication of:

IRWIN MEMORIAL BLOOD BANK
of the San Francisco Medical Society
270 Masonic Avenue
P.O. Box 18718
San Francisco, CA 94118-9990
(415) 567-6400


               EXPLANATION OF THE PATERNITY TEST REPORT 

     Genes  determine  all inherited characteristics.  Genes  come  in 
pairs,  one  inherited from the mother and one from the  father.  Gene 
products  in  the blood include HLA (white Cell) antigens,  red  blood 
cell  antigens, serum proteins and red cell enzymes. Genes  cannot  be 
directly detected but gene products can be identified using laboratory 
tests. By identifying gene products it  is possible to conclude  which 
genes must be present to give rise to these products. HLA typing  will 
exclude  a wrongly accused father 90% of the time. HLA plus  red  cell 
typing  will  exclude  97%. Addition of serum  protein  and  red  cell 
enzymes raises the exclusion to 99.5%.


Phenotyping:
     The  blood of the mother, child and alleged father is tested  for 
the presence of certain gene products or antigens. In this  laboratory 
we  begin  with testing for HLA antigens since this is the  test  most 
likely to provide for HLA antigens since this is the test most  likely 
to  provide a definitive answer regarding paternity or  non-paternity. 
Red  blood  cell antigens are also routinely  tested.  The  phenotypes 
reported  for the mother, child and alleged father are those  antigens 
which are detectable in blood.


Genotyping:
     The  next step is to determine which genes the three  individuals 
must  carry   in order to give rise to these phenotypes.  In  the  HLA 
system we generally identify the products of two HLA genes, HLA-A  and 
B. The HLA-A and B genes from each parent are inherited together as  a 
unit. The combined HLA-A and B gene package inherited from each parent 
is a haplotype.


Obligatory Paternal Genes:
     Inspection  of  the possible genes of the mother and  child  will 
demonstrate which of the child's genes were contributed by the mother. 
The  other  genes  of the child must be inherited  from  the  biologic 
father (obligatory paternal genes).


Exclusion of Paternity:
     The  next  question  is whether the  alleged  father  could  have 
contributed the necessary genes. If the alleged father does not  carry 
the obligatory gene he is excluded. Paternity can also be excluded  if 
an alleged father carries two genes, one of which must be inherited by 
a child who is tested and found to have neither gene. To be certain of 
exclusion  further  tests are done until an exclusion is  found  in  a 
second genetic system.

Probability of Paternity
     If  the  alleged  father is not excluded, the  next  step  is  to 
determine  the probability of paternity. The probability of  paternity 
is the probability that a man with the phenotype of the alleged father 
would contribute the required genes compared to the probability that a 
random  male  from  the same ethnic group would do  so.  Dividing  the 
probability that the alleged father contributed the required genes  by 
the  probability that a random male from the same ethnic  group  could 
contribute these genes fives the paternity index.


The California Evidence Code
     In  California, section 895.5 of the Evidence Code now  puts  the 
burden  of  proof on the alleged father if the Paternity Index  is  at 
least 100. Therefore, if HLA and red blood cell typing does not result 
in an exclusion and the paternity index is less than 100, we send  the 
blood samples to another laboratory where experts determine the  serum 
protein  and red cell enzymes types. These results are  combined  with 
the HLA and red blood cell results to give a combined paternity index.


Per Cent Probability

The Paternity Index (PI) can be converted to a per cent probability by 
this formula: PI/ (PI+1).
          Example:       PI = 150
                         Per Cent Probability = 150/151 = 0.993 = 99.3%
          The  resulting  per  cent  probability  is  not  the   final 
          probability. It still compares the alleged father with  only 
          a  single  random  male, and it ignores  all  of  the  other 
          evidence in the case.


Bayes Theorem

     If all of the other evidence in the case can be reduced to a  per 
cent  probability (prior probability), this can be combined  with  the 
probability  based on the laboratory findings to result in a final  or 
posterior probability. The reports include a table which provides  the 
posterior probability in the case for any prior probability the  judge 
or jury may select.


REFERENCES:
1.   Joint AMA-ABA Guidelines: Present status of serologic testing  in 
     problems  of disputed parentage. FAMILY LAW QUARTERLY, Volume  X, 
     No. 3. Fall 1976

2.   Paternity   Testing,   American  Association  of   Blood   Banks, 
     Washington, D.C. 1978

3.   Probability  of  inclusion  in  paternity  testing.  A  technical 
     workshop.  Silver  H, ed. American Association  of  Blood  Banks, 
     Arlington, VA, 1982.

4.   Inclusion  probabilities  in parentage testing.  Walker  RH,  ed. 
American  Association of Blood Banks, Arlington, VA, 1983. (These  are 
the  proceedings  for the conference held in Airlie House, VA  in  May 
1982,  which confirmed the statistical basis for the  Paternity  Index 
used by this laboratory and required by Section 895.5 of the  Evidence 
code.)

     











































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