Can You Use Your Brother’s DNA to Determine Your Biological Father?
So, can you use your brother’s DNA to determine your biological father? The answer is yes, with a significant degree of accuracy. This approach can be particularly useful for families seeking clarity about their genetic heritage and for legal purposes such as paternity testing. While not conclusive, this method can provide strong evidence that can lead to a court order.
Understanding the DNA Inheritance Process
When two individuals share a parent, they typically share approximately 11-12 chromosomes if they share just one parent. If both parents are shared, the number of shared chromosomes is closer to 23. Although there can be some deviations, if the number of shared chromosomes is close to 23, it can give you sufficient evidence to pursue a court order for paternity.
Popular Commercial DNA Testing Options
If you're in the United States and considering this route, you can use any of the two popular commercial DNA tests—Ancestry, 23andMe, Family Tree DNA Family Finder test, or My Heritage. Each of these tests can cost around $200, though discounts may be available.
These tests will provide you with a list of DNA matches, and your sister (or other sibling) should be at the top of that list—the closest match. If you use 23andMe, the amount of DNA you share will be reported as a percentage. If it's close to 50, you're likely to be full siblings. If it's close to 25, you're likely to be half-siblings. Other companies measure the amount of DNA shared in centiMorgans. Half-siblings typically share about 1600 cM.
Uploading Results for Comparison
To confirm the results more accurately, you can upload the test results from both you and your sibling to the free GEDmatch website. Compare the results one-to-one and check the box that includes the graphic. This will show the matching segments on each chromosome, with blue showing the shared segments from one parent and green showing the full identical matches from both parents.
For full siblings, approximately one-quarter of your tested genome should show full identical matches. Here’s a visual representation:
Example: Full Siblings
Example: Half Siblings
Calculating the Likelihood of a Common Biological Father
To further verify if you and your brother have the same biological father, you can use the calculation method provided by Dr. Blaine Bettinger. This method involves a more detailed analysis of DNA segments and can provide even stronger evidence.
For more detailed information, you can refer to Dr. Bettinger's August 2017 Update to the Shared cM Project.
In conclusion, the method of using your brother’s DNA to determine your biological father is highly effective and can provide significant evidence for paternity testing. However, it’s always advisable to consult a legal professional to explore further steps after such findings.
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