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cookerg t1_iwdeww2 wrote

Both the sperm and the egg carry a random half of the respective parent's DNA, so you get half from the mom and half from the dad. So you can get an approximately 50% different mix from your sibling who is not an identical twin.

(There are slightly different details for mitochondrial DNA and the X or Y chromosome from the father.)

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WDYDwnMSinNeuro t1_iwek0ir wrote

To add onto this, if the only variation were which of each pair of chromosomes you got, that's 2^23 possible combinations per parent. But it's not limited to that, because crossover of genetic material happens at corresponding sites between chromosomes in a pair.

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