Because related possible fathers share some of their genetic markers by inheritance, it is more difficult to distinguish between them than between unrelated possible fathers. For example, a man shares 50% (1 out of 2) of his inherited genetic markers with his biological father, brothers, and sons, and 25% (1 out of 4) of his inherited genetic markers with his biological grandfathers, uncles, nephews, and half-brothers. If two possible fathers are identical twins, then genetic tests cannot distinguish them. The standard statistical analysis of the test results assumes that other possible fathers are not related to the tested man. If there is reason to believe otherwise, then this must be brought to our attention so that appropriate testing and statistical analysis can be performed.
Posted in: Paternity Testing - Basics