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You probably got here from this page. If not, it’s probably a good idea to go look at it and see what this page is about before continuing.

Some of the statistics here won’t actually be viewable at 23andMe. The real purpose of this page is to provide the most accurate possible centiMorgan values for given relationships based on a 23andMe upload to GEDmatch. If you aren’t analyzing an 23andMe kit at GEDmatch for the purposes of investigating possible incest, you’ve probably come to the wrong page.

Table 1. ROH in cM for a given scenario. The number of cM that would be reported for a given scenario at the GEDmatch AYPR tool when using a kit uploaded from AncestryDNA. None of these statistics can be viewed at 23andMe. One must first upload their 23andMe kit to GEDmatch.

Table 2. Shared cM with various relatives when your father is your mother’s son (mother is also paternal grandmother). These values can be found at 23andMe, but first you have to remove any cM from X-DNA matches.

Table 3Shared cM with various relatives when your father is your mother’s brother (mother is also paternal aunt). These values can be found at 23andMe, but first you have to remove any cM from X-DNA matches.

Table 4Shared cM with various relatives when your father is your mother’s father (mother is also sister). These values can be found at 23andMe, but first you have to remove any cM from X-DNA matches.

If you want to see percentages of shared DNA you can go back this page. However, those values will only work with percentages reported at 23andMe if there’s no X-DNA shared, which is not often the case with such close family relations.

Feel free to ask me about modeling & simulation, genetic genealogy, or genealogical research. To see my articles on Medium, click here. And try out a nifty calculator that’s based on the first of my three genetic models. It lets you find the amount of an ancestor’s DNA you have when combined with various relatives. And most importantly, check out these ranges of shared DNA percentages or shared centiMorgans, which are the only published values that match known standard deviations.