Y-Chromosome Test.
This test can prove the paternity of two males within the same paternal lineage, and is typically done when the alleged father is deceased, the alleged paternal grandparents are deceased or unavailable, and there are no other samples available for testing. 

This test can only be performed within the paternal line of the person in question since males receive their Y-chromosome only from the father. The Y-chromosome is passed from father to son relatively unchanged through many generations.  The Y-Chromosome test examines specific locations on the Y chromosome to generate a Y-STR profile for each male tested.  Males who are related through their fathers will tend to have the same or similar Y-STR profiles, and males who are not related will likely have different Y-STR profiles.
Two (2) or more males are required for this test.  Average turnaround is about 9 business days from receipt of all samples.