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How to tell if two brothers are related using DNA tests?

Replies: 3

Re: How to tell if two brothers are related using DNA tests?

Posted: 1381742119000
Classification: Query
Unless you're identical twins, you should share similar, but not exact, admixture or ethnicity results. However, as noted many times in several threads, ethnicity results should be viewed as entertainment and not considered an absolute indication of heritage because each testing company has its own interpretation of results. If you load your raw results at GEDMatch, for instance, you will have access to about a dozen different admixture tools, each with various ethnic categories.

More telling is that as full siblings, you should share a very significant number of cMs across chromosomes. For example, I share 3383.63 cMs with my mother, the longest of which is a string of 267.21 cMs, but I share 2392.58 cMs with my brother and our longest segment is 176.25 cMs.

The attached chart suggests that I should share about 50% of my mom's DNA and about the same with my brother, but my brother and I actually share a little less than 50% and according to my research, it looks like I may favor my mom while he favors my dad.
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allycat113 1381742119000 
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