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Paternity
Trio versus Mother Absent (Motherless) Paternity Test
This page shows an example of a DNA paternity test performed two ways:
- Mother Absent (motherless) (just the Alleged Father and one child)
- Trio (Mother, Alleged Father and one Child)
We
show this example to illustrate that, in some cases, a mother absent test can
produce an incorrect result if the alleged father is
not
excluded in
the test.
The example below is generic and has been abbreviated to show only 10
markers, so it doesn't get too confusing to look through. The intent is to
show that a completely different result can be obtained with regard to exclusion
or non-exclusion of an alleged father depending on whether or not the child's
mother was also tested.
Why
is it important to test the mother, alleged father and the child?
Test on the left: The alleged father shares
markers with the child as seen in the motherless (mother absent) test on the
left. If you look at the highlighted markers, you can see that the
alleged father possesses all of the obligate markers inferred in
the test. Therefore, in this particular case, the alleged father could not
be excluded.
Test on the right: Once the mother’s DNA
marker information is included, one can see that the obligate markers that need
to be contributed by the alleged father are not present in all marker
systems. Some of the markers attributed to the father in the mother absent
case could only be contributed by the mother (right figure highlighted
markers). The mother's markers are actually identified in
the test. The markers that must be contributed by the father are listed as
“Obligate Markers”. It is clear that the father does not possess six
of the obligate markers as indicated by the X
in the rightmost column.
It is now easy to see that the alleged father, who
was not excluded in the motherless test, is CLEARLY excluded at 6 markers when
the mother’s data is present. If the alleged father was not excluded in
the Trio test, he would possess the complementary markers at the 6 maker systems
that excluded him in this example.
So
how often would one see this occur in the real world?
This can occur in 1 in several hundreds to 1 in several thousands random,
unrelated men of the same race, when a mother absent test is
considered. When the mother is also tested, the probability changes to 1
in tens of thousands to 1 in several millions of random, unrelated men of
the same race. These numbers can vary depending on the relative
rarity of the markers present in the father and whether the rare markers were
inherited by the child. Lets put this into perspective.
-
One in several hundreds to several thousands means that more
than one man within a neighborhood or within a small town may be not
excluded as a potential father.
-
One in tens of thousands to several millions means that
fewer than one man in a large city to less than 10 men in the USA would be
not excluded as a potential father.
Obviously, the latter case is much more accurate.
Motherless (mother absent) tests can be done and the result is OK if the alleged
father is excluded at two or more markers. The test is not as reliable if the
result indicates that the alleged father is not excluded. The mother absent test
should be reserved for extreme cases in which the mother is truly not available
for testing.
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