An avuncular test is done to determine if a child is biologically related to a sibling of the alleged father (or mother). However, aunts and uncles will only have 25 % of their genes in common with a niece or nephew. This test cannot provide a result that is as accurate as a paternity test due to the two-fold dilution of genes. This test will provide a numerical probability for the alleged biological relationship.
As in all relationship testing, the sample of a common parent (normally the mother) is always recommended.