Grandparent DNA testAn Avuncular DNA Test is one in which the genetic material (DNA) of a child is compared to that of another individual to determine the likelihood that the other individual is related to the child as a biological aunt or uncle.  The term “avuncular,” which means “resembling an uncle,” was originally used by parentage testing experts when unusual paternity test results suggested that the biological father of the child was really the brother of the man who was tested.

In most cases, avuncular DNA tests are performed to determine paternity—whether or not the biological brother of a tested individual is the biological father of a child—in situations where the possible father is deceased, incarcerated, unwilling or otherwise unavailable to participate in a paternity test.  In a legal setting, avuncular DNA test results could been used to establish paternity of a child in order to acquire custody, to obtain Social Security survivor benefits, to settle an estate/inheritance claim, or to provide evidence of biological relationship between a U.S. immigration applicant and their U.S. citizen sponsor.

Because a child inherits exactly half of its genes from its biological father, and because the biological father shares (on average) half of his genes in common with his full sibling, the child will share (on average) half of its paternal genes in common with the full sibling of the biological father by inheritance.  In an avuncular DNA test, we are asking the question, Does the DNA of the alleged father’s full brother (or sister) contain the genes that the child inherited (or possibly inherited) from its biological father?” Based upon the number of genetic matches observed between the child and the alleged uncle/aunt, and upon the statistical strength of those genetic matches (the likelihood that they would occur by random chance), the laboratory calculates the statistical likelihood that the alleged aunt/uncle is the biological aunt/uncle of the child versus being unrelated to the child.  If the laboratory reports a probability of 99% or greater that an uncle/aunt relationship exists, this is generally accepted to be a scientifically conclusive result.

It is important to understand that, with avuncular tests, it may not be possible to achieve a conclusive result.  The reason for this is that, even though they have the same parents, a full sibling of the alleged father is not genetically identical to the alleged father and may have inherited numerous genetic markers that the alleged father did not.  On the average, testing an alleged father’s full sibling allows us to determine only half of his genes.  To increase the certainty of the results, testing the mother of the child is strongly recommended, as it allows us to identify genetic markers of the child that were inherited maternally and to eliminate them from consideration as possible paternal markers.  We do not recommend performing avuncular DNA tests if the mother of the child is unavailable, due to the substantial likelihood that the results will be inconclusive.

There is, however, one type of avuncular DNA test in which the likelihood of achieving a conclusive result is almost always very high:  when the relationship being tested is between two males—a male child and his alleged paternal uncle.  For such relationships, a specialized type of DNA testing—called Y-STR or Y-chromosome typing—can be performed.  The Y-chromosome is a DNA structure found exclusively in males and passed from a father to each of his biological sons.  As a result of this pattern of inheritance, full brothers of an alleged father inherit the same Y-chromosome as the biological sons of the alleged father.  Therefore, if an avuncular DNA test involving a male child and the full brother of the alleged father demonstrates that their respective Y-chromosome markers do not match, then the alleged father can be conclusively excluded as the biological father of the child.  However, if their respective Y-chromosome markers do match, then the likelihood that alleged father is the biological father of the child will usually be more than 99%.   Because Y-chromosomes are not found in females, Y-chromosome testing cannot be used to address uncle/niece, aunt/niece, or aunt/nephew relationships.

For more information about avuncular DNA tests, please call us today at 1-714-648-0468.


 By: Dr John Taddie