Identical by state
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 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. IBS segments result in false-positive match predictions with autosomal DNA tests.
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?.
Phasing is necessary in order to distinguish between IBD and IBS segments.
- FTDNA definition of identical by state Family Tree DNA Learning Center
- Wheaton K. atDNA matches. Lesson 9 in the series "Beginners' Guide to Genetic Genealogy", Wheaton Surname Resources website, 2013.
- Cooper K. The ABCs of DNA - IBD vs IBS vs mIBC Kitty Cooper's DNA Genealogy blog, 30 January 2012.
- Turner A. "Satiable Curiosity: Identity Crisis: Identical by State or Identical by Descent?" Journal of Genetic Genealogy Fall 2011, Volume 7.