What Is The Best DNA Test To Tell If Two Brothers Have the Same Father?


Twin DNA testing Y-STR MALE LINEAGE If you've got two brothers and aren't totally sure if they have the same biological father, a Y-STR DNA test can provide the answers you need.

But testing brothers does require some extra thought. Let's break it down how Y-STR DNA testing works and the options for finding out if your two brothers share a daddy.

How Does Y-STR DNA Testing Work?

Y-STR DNA paternity testing analyzes specific genetic markers called Short Tandem Repeats or STRs. These are sections of DNA with short sequences that repeat over and over. The number of repeats at a location varies from person to person.

By looking at the Y-STR patterns passed down from parents to a child, Y-STR DNA testing can show if a guy is likely the father. If the Y-STR markers match-up between supposed brothers, there's a high chance they share the same daddy.

Advanced math figures out the statistical odds that the man is actually the shared father. A Y-STR DNA test will conclusively indicate with plain yes or no answer if they come from the same male line. This is always the best option, unless the other potential would be dad is a related male of the same male line.

Testing Brothers for Shared Paternity

Brothers get DNA from the same ma and pa, therefore their DNA profiles will naturally overlap some is simply doing a sibling DNA test. Brothers with the same father will share the exact same Y-STR markers versus brothers with different dads.

But unless they're identical twins, bros still have unique DNA profiles that can be told apart and compared.

There are two main options for testing brothers to see if they've got the same bio pop:

Option 1: It's Best To Perform A Y-STR DNA Test

The simplest way is to have each bro tested together. Their DNA profiles can then be directly compared to see if their Y-STR markers match or differ.

If the bros share the same father, their results should show matching Y-STRs, and thus prove they share the same father.

If the brothers have different dads, their Y-STRs will not match between them and prove they do not share the same father.

Therefore, the lab can break down the exact matching DNA markers to conclude if the bros likely share a daddy or not very conclusively every time.

Option 2: Perform A Sibling DNA Test

The more traditional way of comparing two potential siblings is by preforming either a half sibling DNA test or a full sibling DNA test.

This test however can be less affective, in that it must also bring into play the mother's DNA when doing the analysis.

Sibling DNA testing can be limited in that sometimes the two brothers may have their main DNA pointing to opposite parents, and can thus reduces the level of conclusiveness.

So whenever possible a Y-STR DNA test is usually by far the best option for your answer.

3 Simple Tips for Accurate Brother/Brother Tests

To get the most accurate DNA test results when checking if two brothers have the same dad, keep these 3 simple tips in mind:

  • Include the mother's DNA whenever possible if you perform a sibling DNA test instead of a Y-STR DNA test. Comparing the bros' DNA to their mom's distinguishes maternal and paternal genes for a clearer picture of shared DNA from a common father.
  • Use only an AABB accredited lab with proven expertise in relational DNA testing. Not all labs are equipped to handle the complex math required for brother/brother comparisons. Beware of out of country labs offering cheap low quality 16-22 marker DNA tests.
  • If you're not sure, contact the lab and provide background info about the supposed family connections.  This can help analysts to determine the best test for your familiar situation.

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