How to check that a brother/sister is a biological brother/sister?

Knowing that siblings share around 50% of DNA, it is quite easy to do a DNA test to check whether two people are siblings or not. The company 23andme provides a DNA test that is tailored to find the origin of your ancestor in the first place, but it can also be used to find your DNA relatives.

Order 2 kits from 23andme. You will receive 2 test tubes. The two siblings should spit in their respective test tubes before sending it back to the lab.

When the data are uploaded to the database, the two DNA results will be compared. The percentage of shared DNA between the two persons will appear under the menu “tools” DNA relatives.

How to understand the results?

  • If the two siblings are sister/brother, brother/brother, sister/brother, there should be a record saying that the sibling shares around 50% of DNA
  • If the two siblings are half siblings like half sister/half brother, there should be a record saying that the sibling shares around 25% of DNA
  • If there is a record saying that they share 12,5% of DNA, it means there are cousins.

Advice

It is recommended to order the two kits at the same time so that you can have one access for the two kits. Keep in mind that after you get the results from 23andme, they will not send you an email saying that you are siblings. You have to visit the “DNA relatives” page to know it. Then, you will be able to see the percentage of shared DNA with your sibling which will tell you if you are a DNA relative or not.

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How to check that a brother/sister is a biological brother/sister?
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How to check that a brother/sister is a biological brother/sister?
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Knowing that siblings share around 50% of DNA, it is quite easy to do a DNA test to check whether two people are siblings or not. The company 23andme provides a DNA test that is tailored to find the origin of your ancestor in the first place, but it can also be used to find your DNA relatives.
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