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Why Test the Biological Mother?

Stronger results.

Including the biological mother in any DNA paternity test strengthens test results. Wherever possible the mother should submit DNA samples as a participant. Testing the mother's DNA increases the likelihood of a conclusive result for any DNA test - including DNA tests for paternity, siblings, or grandparents.

WHY INCLUDING THE MOTHER PRODUCES STRONGER RESULTS

A DNA paternity test analyzes up to 15 locations looking for matches between the alleged father and child. All markers must reflect a match (or mutation) or the alleged father is not the biological father. Each match receives an paternity index value indicating the strength of the match; the more unique the match, the higher the index. The probability of paternity is calculated using all of the paternity index values.

Most DNA paternity tests that examine only an alleged father and child show a conclusive probability of paternity: usually 99.99% when the alleged father is included as the biological father or 0% when he is not the father. In some cases, the matches between an alleged father and child provide an inconclusive result. In such instances, IDENTIGENE requests DNA samples for the biological mother. If she is unavailable, the test result remains inconclusive. With the mother, DNA paternity testing almost always provides a strong, conclusive result. Even when results are conclusive, including the mother further strengthens the DNA test conclusion.

Case Studies

For example, consider the following case:

LocusBiological Mother
(not tested)		Alleged FatherChildParentage Index
D2S1338--12, 1310, 121.845
D2S1358--8, 1111, 142.714
D8S1179--21.2, 3219, 21.22.675
D19S433--15, 1812, 157.338

In this case, the probability of paternity is 98.2896% (the product of all the parentage indexes). The result is inconclusive (because it must be greater than 99% or 0%), yet the alleged father and child match at all locations. Now, add the biological mother's sample to the DNA paternity test:

LocusBiological Mother
(Mother A)		Alleged FatherChildParentage Index
D2S13388, 1012, 1310, 123.489
D2S135814, 178, 1111, 145.114
D8S117915, 1921.2, 3219, 21.23.619
D19S4338, 1215, 1812, 1515.309

The probability of paternity increases to 99.9541%. Why? In the first example, one of the two markers from the child and alleged father match at each location. However, we don't know which of the child's markers comes from his mother and which must come from his father. By testing the child's mother, we see which of the child's markers must have come from the father. In the second table, the paternity index is increased.

Not only does the child match the alleged father, but the match is with the marker that must have come from the child's true biological father (since we can see which marker came from the child's mother). In fact, the index value is higher at each location because the biological mother participated in the DNA test.

But, what if the mother's DNA produced different markers?

LocusBiological Mother
(Mother B)		Alleged FatherChildParentage Index
D2S13388, 1212, 1310, 120.000
D2S135814, 178, 1111, 145.389
D8S117921, 21.221.2, 3219, 21.20.000
D19S43312, 1515, 1812, 150.786

With this data, the probability of paternity becomes 0%. The alleged father is not the child's biological father. The biological mother must match the chlid at all locations. We can see that this alleged father does not truly match the child's markers that must have come from the child's true biological father. In some places where he appeared to match the child's markers, the markers clearly come from the biological mother.

Note that there are still some matches between the alleged father and child. If this alleged father is truly the biological father, he must match at all locations (almost any two people will have at least some matches, but a father-child relationship will show matches at all locations). Even a few mismatches can be enough to exclude the alleged father from being the child's biological father. In this case, DNA testing the biological mother turns an inconclusive result to a definite "no" - this alleged father cannot be the child's biological father.

IMPORTANT: Including the biological mother in any DNA test, even grandparent or sibling DNA testing, similarly strengthens the DNA test results probabilities.

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For assistance. more information, or to place your order by phone, call 1-800-DNA-TYPE (800-362-8973).

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