Y Chromosome (Per Person)

The Y chromosome is male specific and passes through generations unchanged from father to son. In a circumstances where an alleged father is unavailable for testing or deceased, a male child can be tested against any number of his male relatives including, but not limited to, other known male children.(Brothers, and half brothers with the same father, uncles, grandfather, and grandfather's brothers).

Since the Y chromosome is only found in males, this type of testing is not useful for female off-spring. Similarly this test is not iron clad for paternity in circumstances where there are two related alleged fathers.