Paternity tests are often something that is followed suit by an interesting, albeit controversial, story. The paternity testing facility commonly receives reports about a customer requesting a paternity test between two separate possible fathers. And yes, that also applies to biologically related fathers. The likelihood of errors sprouting up when testing biologically related fathers can increase the closer they are from being related. Distant cousins are less likely to produce errors as opposed to brothers.

The problem with biologically related paternity testing is that their DNA would have some similar strands that could prove to be difficult to break down. Although a person’s DNA is entirely their own, even twins can have varying results depending on the DNA strand that was tested. However difficult the testing may be, experienced labs can run extended DNA testing using a more in-depth analysis to finalize a proper conclusion. In addition, you can even do so with only one of the biologically related fathers, should the other disagrees with being tested.


Brothers may share the same gene pool that they derived in (parents), but that does not mean that they would result in having the same overall DNA mixture. The DNA between 2 brothers are still distinct enough to warrant clear differences when tested. It is highly unlikely that two brothers would result in the same genetic marker to the child.

Although, it would be best that you still have both possible fathers to attempt the paternity test. The likelihood of any errors is small but there is still a chance. This could also be used to test out other genetic markers that both fathers might share with the child.


There are two types of twins identical and fraternal. Both types of twins would result in significant differences when primed for a paternity test.

Fraternal Twins

These types of twins are siblings that are born on the same day but look completely different from each other. This type of sibling relationship is easier to identify when it comes to a paternity test.

The DNA between the two fraternal brothers would be diagnosed as a regular non-twin brother relationship. Due to the significant difference in genetic structure, there is no need to worry about a high chance of failure in the testing process. As usual, it is highly advised to persuade both twins to take the paternity test alongside the mother to fully analyze the genetic markers of the child’s health.

Do note that you should inform your DNA testing faculty or doctor that the fathers in question are fraternal twins, that way the proper additional testing procedure will be applied.

Identical Twins

Identical twins are exactly as the name suggests, two siblings with the same genetic features and DNA code. The process of differentiating the DNA between the two identical twin brothers is an arduous process. Even the most advanced piece of scientific hardware to date can still not fully and effectively differentiate between the two samples.

Further testing must be applied. In addition, you might be forced to repeat the same tests over and over in hopes that there could be a mismatch that the scientists can discover.

Father And Son

The simple genetic math on an offspring is 50% genetics from the father and 50% genetics from the mother. An equal divide as all things should be. However, a paternity test between two fathers that are biologically linked at as father and son have a strong chance of producing a false positive.

This type of procedure needs to be mentioned to the testing facility beforehand and it would be best to have both alleged fathers participate in the testing. Although, you can increase the likelihood of success in the test by having the mother voluntarily agree to be tested as well. That can help isolate the genetics of the offspring to an easier degree. Failure to inform the testing facility of the familial relationship between the fathers could result in a high false-positive result.


The chances of both cousins’ having a matching are extremely minimal to the point that the entire process would be no different from a DNA paternity test done on two complete strangers. Their genetic connection is too far-off that it is virtually impossible to make a mistake between the two potential fathers.

Final Tips

Figuring out the father between to biologically related men can be complicated the more they are closely related. However, you should always keep these tips in mind when conducting a DNA paternity test.

  • Ensure that you can test both fathers whenever possible.
  • Do not be afraid to contribute to the mother’s DNA to speed up the process. In addition, it will also be more accurate.
  • Always inform the testing facility that the fathers in question are biologically related and to what degree.


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