The Build 37 region of chromosome 22 from 16,051,881 to 25,095,451 for a length of 20.82 centiMorgans is a known region of Excess IBD pileups. (See Table 3 at https://dx.doi.org/10.1371/journal.pgen.1004144.)

Genetic genealogists know that if they have triangulations of kits within this region, the matches may be IBS (Inheritance by State) rather than IBD (Inheritance by Descent). That is, while triangulations usually indicate that the three people whose DNA triangulates share a recent common ancestor (which is the case with IBD), if they see triangulations in this region, there may be no recent common ancestor, since they inherited this DNA from an ancient source. Even if they have common ancestors, matching in this region does not necessarily mean that they have inherited the DNA that they share in this region from that common ancestor. So, the response is to ignore matches in this region.

This web page gathers information about this region and seeks to understand it as fully as possible and answer a number of questions.

1. What is the exact series of bases (A, C, G, T) in the raw results that defines this pileup region?
2. Are all subset HIRs within this region also excess IBD?
3. Can there be valid non-excess IBD matches in this region? And if so, how do you know they are valid?