Identity by descent
（重定向自Identical by descent）
![The origin of IBD segments is depicted via a pedigree.](/Images/godic/202501/19/Pedigree,_recombination_and_resulting_IBD_segments,_schematic_representation1541.png")
![An IBD segment identified by HapFABIA in Asian genomes. Rare single nucleotide variants (SNVs) that tag the IBD segment are coloured purple. Below the turquoise bar, the IBD segment in ancient genomes is displayed.](/Images/godic/202501/19/IBD_segment_detected_by_HapFABIA_in_1000Genomes1541.png")
A DNA segment is identical by state (IBS) in two or more individuals if they have identical nucleotide sequences in this segment. An IBS segment is identical by descent (IBD) in two or more individuals if they have inherited it from a common ancestor without recombination, that is, the segment has the same ancestral origin in these individuals. DNA segments that are IBD are IBS per definition, but segments that are not IBD can still be IBS due to the same mutations in different individuals or recombinations that do not alter the segment.