Identity by descent
= Identity by descent
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= IBD
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{synonym}
= Identical by descent
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Allele copies are identical by descent if they derive from the same specified ancestral copy. Identical observed states need not imply this ancestry. Two diploid individuals are 2-IBD when both of their allele copies can be paired as identical by descent; autozygous individuals carrying two copies of the same ancestral copy are mutually 2-IBD when that ancestor is shared.