Identical by state

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Identical by state is a term used in genetic genealogy to describe DNA segments which do not signify the sharing of a recent common ancestor and are therefore not identical by descent. IBS segments result in false-positive match predictions with autosomal DNA tests.

Some IBS segments are spurious segments (pseudosegments) which have the appearance of being a continuous long segment but which are in fact composed of two or more compound segments. For an explanation of compound segments see the Family Tree DNA FAQ I have tested my husband, our child, and myself. Why does our child have matches that neither parent has?.

The techniques of chromosome mapping, triangulation and phasing can be used to distinguish between IBD and IBS segments.

Further reading