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« on: Sunday 12 April 15 15:30 BST (UK) »
Jeanne. Look this up on google and found the following information: Even though siblings share half their DNA, they can share any number of markers in a DNA test. They might match up at all of them or none of them. Or more likely, they will match up at some number in between.
This might seem weird at first. After all, two siblings share half of their DNA. So they should share of half their DNA in a DNA test too, right?
Well this would be true if a DNA test looked at all of a person’s DNA. Unfortunately, very few of them do. Instead, they look at only 15 or 20 out of millions and millions of possible spots.
Because these tests look at so few markers, by chance, one sibling might end up sharing only some DNA at the markers tested. Or they might not share any DNA at all.