Sometimes when people are asking about this they are asking about alleged fathers who are only cousins.  Whether they are first cousins or a relationship more distant this type of relationship is distant enough that the DNA they do have in common will not cause any type of conflict with a paternity test.  So, in this type of scenario there is no need to be overly concerned if both fathers cannot be tested.

People will also call about two alleged fathers who are brothers.  The possibility of this causing problems with the results of a paternity test is higher but not by a lot.  Two people who are full brothers still have very unique DNA profiles.

It is extremely unlikely that two people who are only siblings would match the same child at all the markers tested for paternity.  In a paternity test we generally test fifteen markers and in order to be considered the father one must match at all fifteen. 

To ensure the most accurate  results possible we recommend including both alleged fathers and the biological mother whenever feasible.  This will give us all the opportunity to exclude the correct father and provide ensure the most accurate and complete results. 

If we are not able to test both alleged fathers its important to let us know when you send in the samples that the other alleged father is a brother to the one being tested.  This way we know ahead of time that there may be some markers in common that may not be the case if the alleged fathers were not related.

The only exception to this rule is when the alleged fathers are identical twins.  In this scenario DNA testing will not be able to indicate which of the alleged fathers is in fact the biological father of the child.  So, I hope that this blog helps sets a few fears straight.  If not please feel free to email me at kstyer@identigene.com or call at: 801-462-1465.