So it's 1/2 shared dna for siblings, not 1/4th. Only (I think, possibly) it's 1/... | Hacker News

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Udik on Oct 25, 2015 | parent | context | favorite | on: First reported case of a paternity test fooled by ...

So it's 1/2 shared dna for siblings, not 1/4th. Only (I think, possibly) it's 1/2 on average instead of being exactly 1/2 as in the case of parents and children.

jfoutz on Oct 25, 2015 [–]

Ah, I did the table wrong in my head. You're right. 2 genes, one from father one from mother, sibling A along the top, simbling A down the side.

       MM MF FM FF
    MM  1 .5 .5  0
    MF .5  1  0 .5
    FM .5  0  1 .5
    FF  0 .5 .5  1

(4+ .5 * 8 + 0)/16 = 8/16 = 1/2

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