07/09/2026
Does this help
Explain why siblings don’t share the same DNA?
🧬 Two brothers take the very same DNA test, get noticeably different results, and one of them rings the company to complain. Nothing has gone wrong anywhere. That is simply how it works.
You get half your DNA from each parent, but not the same half your brother got. When a parent's DNA is passed on it is shuffled first, in a process called recombination, and the deck is cut differently every single time. So full siblings share about fifty per cent of their DNA on average, and the real figure ranges roughly from the low forties to the high fifties. Average is not the same thing as always. 🔀
Which means the pieces you inherited from any one grandparent are not the pieces your sister inherited. You might carry a long stretch from your father's mother and your brother might carry almost none of it. Go back four or five generations and it is entirely normal for a distant ancestor to have handed measurable DNA to you and none at all to your sibling. They are still your ancestor. The DNA just did not come down your particular road. 🌿
That is why the ethnicity percentages come out different between brothers and sisters, sometimes by ten points or more, and why one sibling can match a cousin on a testing site while another does not match that same cousin at all.
The use of knowing it is real. If you are working on a family line, test your siblings as well as yourself. Between the lot of you, you are holding a good deal more of your grandparents' DNA than any one of you holds alone. ☘️