DNA Worldwide’s RGPNE improves statistics for Grandparentage DNA Testing

By: Terrence Ogden


It is not uncommon that an alleged father of a child in question is unavailable for paternity testing but that the parents of that alleged father (i.e. the child’s alleged grandparents) are available. In these cases, it is often possible to utilize the power of DNA to conclusively determine if a son of those alleged grandparents is the biological father of the child in question.

All individuals are comprised genetically of DNA passed down from their parents. In fact, one-half of our DNA came from our mothers and the other half came from our fathers. We do not carry DNA from anyone else! Therefore, if we wish to determine if a certain man is the father of a child (or a woman is the mother of a child, for that matter) but that man is not available for genetic testing, we can look at his two parents to determine if they could have produced a son who is the biological father of the child.

In other words, we can reconstruct the genetics of the alleged father using the genetics of his parents and then ask whether he could be the biological father of the child. This is why our genetic grandparentage test reports reflect a paternity index rather than a “grandpaternity index.” Though we are testing alleged grandparents, we are really looking at a genetic reconstruction of their son and determining the likelihood of paternity.

When we test a child and his mother we can determine, in most cases, the paternal genetic contribution – in other words, what the father’s DNA should look like genetically. If we test a pair of alleged grandparents we can determine whether they carry the paternal DNA present in the child. If, at all markers tested, either one (or both) of the two alleged grandparents carries the paternal DNA present in the child, we can state that “a son of the alleged grandparents is not excluded as the biological father of the child”. In such cases, we have built a strong genetic argument that the alleged grandparents produced a son who is the biological father of the child. This is a very powerful test and can provide conclusive resolution in the majority of cases.

However, there are instances where the power of grandparentage testing is more limited. In annother article, we discussed the importance of examining the mother of the child in question in DNA paternity testing. The same principle holds true for grandparentage testing. When genetic information from the mother is not obtained, it is impossible in most cases to determine with certainty the paternal genetic contribution to the child. This uncertainty diminishes the power of the statistics that the laboratory can generate in cases where the alleged grandparents are not excluded AND it decreases the probability that the laboratory will be able to exclude a pair of alleged grandparents that are not the biological grandparents. In other words, it is a weaker test without the mother.

To help determine whether a test has produced genetic data strong enough to exclude alleged grandparents who are not the true biological grandparents (a crucial requirement of any reliable genetic test), a new genetic testing statistic was developed by DNA Worldwide scientists at Sorenson Genomics called the Random Grandparents Not Excluded (RGPNE) value. The RGPNE is calculated as part of every grandparentage test we perform and illustrates the importance of testing the biological mother of the child in question in grandparentage cases because RGPNE values are much less significant when the mother is not included in the test. We, therefore, strongly recommend that every effort be made to include the mother with your grandparentage test: it offers the best chance of getting conclusive results.

Finally, though it is possible to conclusively determine biological grandparentage when only one of the two alleged grandparents is tested, it is not possible to conclusively exclude a pair of alleged grandparents when testing only one of them. Therefore, every effort should be made to test both alleged grandparents to ensure we give the test the greatest likelihood to succeed.

In summary, we can reconstruct what the genetics of the alleged father may be using the genetics of the alleged grandparents and then ask whether the reconstructed alleged father is the biological father of the child in question. This is a very powerful genetic test that almost always produces conclusive results when we test both alleged grandparents and the mother of the child. If each of these individuals cannot be tested, it is still usually worthwhile to perform the test without them but we need to keep in mind that the test will likely not be as powerful as it could be. Talk to a DNA Worldwide DNA Test Consultant to learn more.


Terrence Ogden is an investigative writer. For more information on DNA paternity or ancestry testing in UK or DNA testing kits, he recommends you to visit www.dna-worldwide.com/