According to 23andme, my younger brother and I (male) matched 64.2% with 4776 cM. That seemed weird since our matches with our parents are the normal ~50% or just under.

This is very much not my field, but from googling my best guess is I've misunderstood something, as it seems extremely unlikely that we are extremely unlikely (like, 4-sigma) outliers.

Is there a simple explanation I'm missing here?

Maybe it's because 23andme counts % differently, but it's hard to make sense of it all. In case it matters, we have 3225 cM (41 seg) half identical, 1551 cM (50 seg) full. I'm guessing the full is counted where it shouldn't be?

  • Seems likely to be a mistake... is there any chance your parents are distantly related? That could push the number up.
    – Charlie
    May 7, 2021 at 15:35
  • I doubt they are enough to matter. No known crossover, 0% between them on 23andme, from different areas hundreds of years back... could there have been a mistake with one of our DNA kits or something? And that doesn't explain why each of us gets perfectly reasonable results against everyone else.
    – Trev
    May 7, 2021 at 15:44
  • 2
    Try comparing you and your brother on GEDMATCH (one to one analysis) and see if you get the same value
    – Charlie
    May 7, 2021 at 15:45
  • Unfortunately, he's not too keen on throwing his DNA code around the internet, so I can't try that.
    – Trev
    May 9, 2021 at 0:12


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