Question about ancestry DNA results for siblings with same biological parents


#1

My brother and I are thinking of taking an ancestry DNA test? Given that we have the same biological mother and farther, would the results be identical?


#2

Your DNA is not identical, unless you are identical twins. As you did not mention that you have an identical twin, I will assume that you are not identical. In which case, you each get 50% of your DNA from each parent. But event this is not 100% accurate, and I will explain why. All human genomes are between 99% and 99.9% identical. So the 50% difference between sibling genomes is actually 50% of that 0.1-1% difference (https://www.ncbi.nlm.nih.gov/pubmed/20471132). More so, if two siblings would be of different sex, the male will have access to the patrilineal ancestry of the Y chromosome, which the female won’t have.


#3

I recently came across an article which explains how DNA is passed down from generation to generation. You can read the full explanation, here: https://genetics.thetech.org/ask-a-geneticist/same-parents-different-ancestry


#4

Unless you are identical twins, then it is very unlikely, almost impossible for the results to be identical. This is because each of you inherited 50% of each of your parents’ DNA. Based on probability, it’s impossible for two siblings to have inherited the exact same 50% from each parent. There is indeed a lot of overlap which will show up in your ancestry DNA results. In the same way the difference will be identified. Let’s say you have a parent with a high percentage of Eastern European ethnicity. It is likely that both you and your sibling inherited a considerable percentage of this. This percentage might not be the same size, so you might have 24% Eastern European, while your brother 32%.