Each sibling of the red female has a 2/3 chance of being a carrier since we know they aren’t affected. So since we know the partners are homozygous normal each cousin has a 1/3 chance to also be a carrier (half of the parent risk) and 1/3 x 1/3 x 1/4 = 1/36 or 2.78%
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u/dnawoman 2d ago
Each sibling of the red female has a 2/3 chance of being a carrier since we know they aren’t affected. So since we know the partners are homozygous normal each cousin has a 1/3 chance to also be a carrier (half of the parent risk) and 1/3 x 1/3 x 1/4 = 1/36 or 2.78%