When asked about including the mother in DNA paternity testing, many people respond by saying something like, “But I already know I’m the mother. Why would I test?”
Having the mother submit her samples along with the child and possible father can actually help HomeDNA Paternity answer your paternity questions with more certainty, which is why we include the mother’s participation is included in the lab fee.
Strengthening DNA Paternity Testing Results
Testing the biological mother’s DNA increases the chance of a conclusive result for any DNA test-including DNA tests for paternity, siblings, or grandparents. That’s why the mother is strongly encouraged to participate in any DNA relationship test (excluding maternity testing) at no additional cost. In fact, each kit includes collection materials for the child, possible father, and mother. In most cases, the mother’s DNA is not needed to strengthen results, but sometimes it is. If it turns out her DNA is required and it was not submitted, it will delay results, which is an inconvenience and extra stress no one wants. So if it’s possible to submit the mother’s DNA, why not? Here are the details on why it can be important.
How the Mother Strengthens DNA Paternity Testing Results
A high-quality paternity test checks 2o Genetic Systems (sometimes called markers or locations), and more, if necessary, looking for matches between the possible father and child. If he is to be considered the biological father, each location must show a match (with the exception of instances of a mismatch due to naturally-occurring mutations).
Each match is assigned a number (Paternity Index) which shows just how strong the match is: the higher the number, the stronger the match. All of the indexes are multiplied together to produce the Combined Paternity Index (CPI). If he is the biological father, the CPI must be at least 100 (at least 200 for immigration cases).
Paternity testing with just a father and a child usually produces a high CPI and a very high Probability of Paternity (usually 99.99% or greater if he is the father). However, sometimes the matches between father and child aren’t strong enough for conclusive results. In these rare cases, HomeDNA Paternity asks for the DNA samples of the biological mother. With the mother’s information to go along with the possible father’s, DNA paternity testing almost always provides a strong, conclusive result. Even when results are already conclusive, including the mother strengthens the result.
A Paternity Test Example
Consider the following paternity test example:
In this case, the probability of paternity is only 98.99% (multiplying together all the relationship index numbers). The result is inconclusive because it must be greater than 99%-even though the father and child match at each location.
Now, let’s add the biological mother’s sample to the DNA paternity test:
The probability of paternity increases to 99.90%-a conclusive result showing that the father really is the biological father of the child.
Why does Including the Mother Help?
In the first example, all of the locations match, but we don’t know which of the child’s DNA markers comes from his mother and which comes from his father. Since the mother wasn’t tested, each relationship index is lower than it could be.
By testing the child’s mother, we see which of the child’s markers must have come from the father and this makes each match stronger. In the second table, the Paternity Index numbers are higher and the result is now conclusive because the Probability of Paternity is higher than 99%.
The Mother Won’t Agree to Participate. Is it Still OK to Test?Yes, absolutely. Although the mother’s participation can strengthen results, her DNA is not usually needed in order to obtain conclusive results. But if she can provide her DNA and is willing to do so, that’s ideal…just in case!
And remember: Including the biological mother’s DNA is not just for straight DNA testing. She should be included in any DNA test, even grandparent DNA tests or sibling DNA testing, in order to strengthen the DNA test results.
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