Identity by descent
A DNA 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 the segment is maximal, that is, it is delimited at both ends by ancestral recombination events. == Theory == All individuals in a finite population are related if traced back long enough and will, therefore, share segments of their genomes IBD. During meiosis segments of IBD are broken up by recombination.