- Double first cousin
Double first cousins arise when two
sibling s reproduce with another set ofsibling s and the resulting children are related to each other through bothparent s' families. Double first cousins share both sets ofgrandparent s in common and have double the degree ofconsanguinity than ordinaryfirst cousin s. Genetically they are as related as half-siblings. Their coefficient of coancestry is 1/8th or 0.125. While double first cousins have the same coefficient of coancestry (1/8) as half-siblings, they do have higher chances of sharing "both" alleles (1/16 vs 0) and lower chances of sharing one allele (3/8 vs 1/2) with each other than half-siblings.When
identical twin s reproduce with identical twins the resulting children are genetically indistinguishable from full siblings, although they are legally double first cousins. When identical twins reproduce with siblings the resulting children are more related than half-siblings but less related than full siblings, although they are also legally double first cousins.Children of double first cousins are double second cousins to each other.
ee also
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Parallel cousin
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