Paternity Testing

Do I need to include Mom in a paternity test?


Accurate DNA paternity test results can be reported without the biological mother participating, but including her in the paternity test can strengthen the results. Whenever possible the mother should be included in DNA testing.

How does including the mother help in paternity testing?

DNA paternity testing analyzes 15 Loci or markers (locations) on the DNA to determine if there are matches between the alleged father and the child at each location. If there are matches, each match receives a paternity index value which is used to calculate the combined paternity index and gives the probability of paternity (usually 99.99% when the alleged father is included as the biological father, or 0% if he is excluded).

Most paternity tests with only the alleged father and child participating do show conclusive results, meaning we have enough information to report conclusively or simply put, a yes or a no answer. There are occasions when the matches between the alleged father and child are inconclusive. This happens when the calculations involved could not get the probability of paternity above 99%, although there are matches. If this does happen, Identigene will ask for the biological mother’s sample to be included in the paternity test. If the mother is not willing or is unavailable, the results will remain inconclusive. Including the mother almost always gives conclusive results. We strongly recommend including the biological mother in any DNA test, including grandparent, avuncular, and sibling DNA testing.

“Why Test the Mother” Here is an example that we use to demonstrate how the mother’s profile helps strengthen paternity test results:

Locus Biological Mother
(not tested)
Alleged Father Child Parentage Index
D2S1338 12, 13 10,12 1.845
D2S1358 8,11 11, 14 2.714
D8S1179 21.2, 32 19, 21.2 2.675
D19S433 15, 18 12, 15 7.338

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

Locus Biological Mother Alleged Father Child Parentage Index
D2S1338 8, 10 12, 13 10, 12 3.489
D2S1358 14, 17 8, 11 11, 14 5.114
D8S1179 15, 19 21.2, 32 19, 21.2 3.619
D19S433 8, 12 15, 18 12, 15 15.309

 In the second table, the paternity index is increased and 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.

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.

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