DNA relationship testing can be used to confirm the existence of biological relationships between relatives. Types of relationship tests include sibling or siblingship DNA testing, avuncular DNA testing, and grandparent or grandparentage DNA testing.
Sibling DNA Testing (or siblingship DNA testing) is used to determine whether two alleged siblings have biological parents in common when the parents are not available for testing. Sibling tests are used to provide additional evidence of family relationships in situations where the alleged father is unavailable for a paternity test. They are also used in verifying biological family members of an adoptee or siblings who were separated at birth. There are two types of sibling tests:
- A full sibling test is designed to establish if two individuals share both biological parents.
- Half sibling test is designed to establish if two individuals share one biological parent in common, either the mother or the father.
Avuncular DNA testing is like a paternity/maternity test where certain specific DNA markers are analyzed to determine the statistical probability that a person is the aunt or uncle of a child, instead of determining a direct parental relationship. The test can also be administered between an alleged aunt or uncle and an alleged niece or nephew. DNA Testing with a possible brother or sister of the possible father (the possible aunt or uncle) can help answer paternity questions when the possible father is not available to be tested.
Grandparent DNA testing (grandparentage DNA testing) is designed to determine whether an individual is biologically related to an alleged grandparent. This DNA test requires the participation of at least one possible grandparent and the alleged grandchild, although it is always best if both possible paternal grandparents are available for the test. The test is often performed in cases where the child’s alleged father is deceased or unavailable for paternity testing and the child’s grandparents have doubts about whether the child is really related to them. A grandparent DNA test is based on the fact that a child inherits half of his or her genetic profile from each biological parent. When one of a child’s parents is missing or deceased, we can look to the grandparents to determine if they contributed DNA to the child’s genetic profile.
How does DNA relationship testing differ from DNA paternity testing?
Unlike a DNA paternity test, which will always provide a conclusive result, relationship (avuncular/grandparent) DNA tests are different. When these tests are conducted, the laboratory will determine the genetic profile of the alleged relatives. Based on the type of genetic material exhibited by each person, an index is determined. If the index is less than 1.00, this indicates non-relatedness. If the index is greater than 1.00, this indicates that the two tested individuals are more likely to be true biological relatives. The higher the value of the index, the greater the likelihood that the two individuals are true biological relatives.