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How To Interpert DNA Paternity Test Results

posted by DNA Identifiers @ 11:27 AM
Friday, September 11, 2009

By Jessica

Many people think that a DNA paternity test will give a “yes” or “no” answer. The truth is that it is slightly a bit more complicated than that. In the vast majority of tests, either an “inclusion” or “exclusion” result will be reported.

What an Inclusion Means

An inclusion is reported with a probability of paternity (POP) of 99% or more and a match is found at all genetic markers tested. In an inclusion report, it is stated that the alleged father “cannot be excluded” as being the biological father of the tested child. These three words often create a lot of confusion. This wording is used since an inclusion can not ever be reported at 100%. However, the combined paternity index (CPI) should also be looked at, as it can help to make the results more understandable. First though, it should be understood that the bare minimum for reporting an inclusion result is with a POP of 99% and a CPI of 100 (alleged father and child only) or 500 (alleged father, child and mother). Since most laboratories utilizes an advanced analysis of fifteen genetic markers as a standard, they normally see POPs and CPIs far exceed the minimum requirement. So, when the CPI is say, 100,000, it can be interpreted as a 1 in 100,000 (of the defined male racial population) certainty that the alleged father is the biological father of the tested child.

What an Exclusion Means

An exclusion is reported with a POP of 0.00%. In an exclusion result, it will be seen that at at least two genetic markers, there is a non-match. In an exclusion report, it is stated that the alleged father “was excluded” as being the biological father of the tested child. When an exclusion is reported, a second, independent test will be performed to confirm that the exclusion can be duplicated.

Other Possibilities

Another possible result may be an inclusion with a mutation. In most cases, an inclusion result means that at all tested genetic markers, a match is found. However, sometimes an inclusion can be reported when all but one marker has a match (or, in rare cases, two). Known mutations have a specific frequency in various racial populations and, often, that frequency is low. So, when the mutation frequency is figured into the formula for calculating the POP, it can possibly cause the POP to fall below 99%. To confirm mutations, it is always recommended that the mother test, if she has not already, or to perform extended testing of additional markers.

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