If you suspect your partner One of the most popular methods is installing a GPS tracker. Another method that is starting to gain popularity is infidelity DNA testing where you would send in items you suspect may have another persons DNA on them and you find out for certain. Ultimately on your gut level you just know and these other methods are simply confirmation.
Testing a grandparent or an aunt or uncle This test can also be used between siblings to determine if they share one or both parents. These tests can be performed with conclusive results without needing to include the parents DNA. These are all alternate ways to determine paternity.
The Y-chromosome, also known as the Y-STR or also Y-DNA test is a test that can be done between two males to determine if they share the same ancestral paternal line.