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From:
Subject: Re: [DNA] DNA FACT or FICTION?
Date: Sun, 1 Jan 2006 16:34:06 EST
In a message dated 01/01/06 11:35:09 AM Pacific Standard Time,
writes:
> Ann wrote
>
> Hi,
> I was watching a program last week about these two mothers whose children's
>
> DNA did not match the mother. Both mothers had two sets of DNA. The
> explanation that was given was that they should have been twins but one twin
> died or
> did not mature early in the pregnancy.
>
>
> OOh Ann you're the person I've been wanting to ask. Is this something
> standard they look for? My only guilty pleasure is watching DNA tests
> on the Maury Povich show. Some of these women look at 8 guys trying to
> find the father. I've always wondered: Does the DNA testing company
> look to see if the child could be the child of a sibling of the people
> being tested. That could explain negative results with the results you
> mentioned above.
You addressed your message to another Ann, I think, but I'll take a stab at
it anyway. In the case of the chimeric mother, who basically had a mix of DNA
from two siblings (the vanishing twin), the DNA paternity (relationship)
testing did turn out to be what you'd expect to find in an aunt/niece type
relationship. Some but not all alleles were good matches.
In ordinary cases (no chimera), the results for a father-mother-child triad
are virtually certain, even if two brothers are candidates for being the
father. There are two alleles for every marker, one inherited from the father and
the other from the mother. Every allele present in the child *must* be present
in the parents. However, in "deficiency" cases, where the mother is not
available, the results can sometimes be ambiguous. I'm not sure I posted this
abstract before.
=====
Forensic Sci Int. 2005 Sep 2; [Epub ahead of print]
Possible pitfalls in motherless paternity analysis with related putative
fathers.
von Wurmb-Schwark N, Malyusz V, Simeoni E, Lignitz E, Poetsch M.
Institute of Legal Medicine, Christian-Albrech-University of Kiel,
Arnold-Heller-Str.12, 24105 Kiel, SH, Germany.
Nowadays, more and more paternity cases are carried out investigating only
child and putative father, mostly for economical or private reasons. Usually,
reliable results can be obtained and the putative father can be included or
ruled out with a high certainty. Considerable problems might arise when a relative
of the biological father is investigated as being the putative father. In
this study, we investigated 164 persons from 27 families creating artificial
deficiency cases using the AmpFlSTRIdentifilertrade mark kit, which amplifies 15
STRs simultaneously. We analyzed 93 child/biological father pairs and the
corresponding uncles, respectively the brothers of the biological fathers. The
average paternity probability for the biological father was 99.9699% (paternity
index (PI): 3321.26); only in three cases the results were under 99.9%. In five
out of 125 child/uncle pairs no STR mismatches were found and paternity
probabilities between 99.9726% (PI 3652) and 99.9970% (PI 33,545) were calculated.
The average number of excluding loci was 3.4, but in 31.2% of the cases only
zero, one or two mismatches were found. When both putative fathers were
genetically typed, the biological father usually had a statistically higher paternity
probability. Nevertheless, the differences between probabilities for father
and uncle were only small. These results show that a reliable investigation of
deficiency cases (i.e. child and putative father) seems to be more difficult
than generally assumed. Especially in cases with an unknown familiar background
and/or when investigating foreigners for immigration purposes, the laboratory
expert should include the mother, increase the number of investigated loci or
include a second method such as RFLP-analysis, some serological systems or
typing of X-chromosome specific STRs to further ascertain the results.
PMID: 16143476 [PubMed - as supplied by publisher]
=====
If you're interested in learning more about this type of testing, my book
"Trace Your Roots with DNA" has a whole chapter on "Next of Kin," which explains
more about the methods and limitations of relationship testing (a more generic
term than paternity testing).
Ann Turner
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