What is a sibling test?

12 Aug 2017

A sibling test will clarify whether two alleged siblings share the same father. This test, specifically a STR test as siblings are of different sex, is done in cases where the father is unavailable for testing or deceased.

• You can do a half sibling DNA test or a full sibling DNA test

A sibling test is on of several DNA relationship tests. It is of course possible to get an exhumation and collect a DNA sample from the dead alleged father but this is extremely costly and time consuming and in some countries that laws regarding exhumations are very rigid. Technically, a paternity DNA test is always the first option to consider when the father is available for testing rather than the sibling test.

In the case in question, should the daughter of the deceased consent to the test, then scientists will draw up her DNA profile and that of her alleged half brother (we know that they do not share the same mother). Given the fact that they have different mothers, one would expect at least half of their DNA profiles not to match. If they happen to share the same father, then the other remaining half will show common genetic markers which the two siblings inherited from their father. If they do not share the same genetic markers the sibling test it would likely indicate that they are not siblings or unrelated.

Sibling DNA testing involves establishing how much common DNA is found between two alleged siblings. Including the mother’s sample is always important even if the siblings have different mothers (as is the case given above). Having the mother’s DNA sample will help map her genetic pattern and remove her share of genetic inheritance thereby leaving the genetic markers that have only been inherited from the father. This helps towards a more accurate sibling test.