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.
Many of the statistics here won’t actually be viewable at AncestryDNA. The real purpose of this page is to provide the most accurate possible centiMorgan values for given relationships based on an AncestryDNA upload to GEDmatch. If you aren’t analyzing an AncestryDNA kit at GEDmatch for the purposes of investigating possible incest, you’ve probably come to the wrong page. Although, you could use comparisons from AncestryDNA and only compare them to the HIR values in Tables 2-4 below.
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 AncestryDNA. One must first upload their AncestryDNA kit to GEDmatch.
Table 2. Shared cM with various relatives when your father is your mother’s son (mother is also paternal grandmother). Any of the rows labeled HIR + FIR or simply FIR are only for AncestryDNA kits uploaded to GEDmatch, since AncestryDNA counts FIR segments as if they’re HIR segments. Rows with HIR only or no designation are valid for comparison directly on Ancestry’s site.
Table 3. Shared cM with various relatives when your father is your mother’s brother (mother is also paternal aunt). Any of the rows labeled HIR + FIR or simply FIR are only for AncestryDNA kits uploaded to GEDmatch, since AncestryDNA counts FIR segments as if they’re HIR segments. Rows with HIR only or no designation are valid for comparison directly on Ancestry’s site.
Table 4. Shared cM with various relatives when your father is your mother’s father (mother is also sister). Any of the rows labeled HIR + FIR or simply FIR are only for AncestryDNA kits uploaded to GEDmatch, since AncestryDNA counts FIR segments as if they’re HIR segments. Rows with HIR only or no designation are valid for comparison directly on Ancestry’s site.
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.
My mother’s results on the GED Match Are Your Parents Related tool (via her Ancestry DNA) show
Largest segment = 55.6 cM
Total of segments > 7 cM = 589.7 cM
Looking at your charts and from what I’ve sleuthed through her Ancestry matches in my year of research thus far, I believe her parents must have been brother and sister? I’m hoping you can confirm if I’m understanding this correctly, please?
Thank you in advance for your time and expertise!
Hi Christine,
And you didn’t multiply by four to get 590 cMs, right? It’s much more likely that your mother’s father was something like a half-brother, uncle, or grandfather to your maternal grandmother. Given the people in your tree, does one of those scenarios seem plausible? If so, you might be able to investigate through your mother’s matches which sides of the tree show higher cMs. For example, if your mother’s father were your grandmother’s paternal half-brother or paternal uncle, then your mother will likely share higher than normal cMs with descendants of her maternal grandfather’s side of the family and maybe average cMs with her maternal grandmother’s side. I hope that helps.
Thank you so much for getting back to me! I did not multiply by 4. My mom was adopted so this is a huge mystery to us but there are some matches who stand out as having higher than expected cM’s. If you don’t mind another question, would my numbers with them also be inflated or do things kind of work themselves out with the next generation?
Hi Christine,
Your numbers would also be inflated with them, too. The only thing that works its way out in one generation is runs of homozygosity (ROH). That means that, although your mother has high ROH, you won’t have any at all. (It would require your father being related to your mother for you to have ROH.) Expected shared cMs would be higher even several generations later. The only thing is that at some point the cMs are so small and the inflated amount is so small that it would be very difficult to notice. But you should see it very pronounced a couple of generations back. You’ll definitely want to use your mother’s kit and not your own to figure out who her father was.
We have lots of half relationships in our tree and I have dyscalculia. Using the AYRT, one relative gets total 603.7 with largest segment 77.4. The grandfathers 1/2 brother is 787 cm, his son is 537, an uncle 2928 and aunt 2859 that are full to each other, a maternal 1/2 uncle 1495 and maternal aunt 1694, and a half sister is 1920. Would this read as the persons grandfather, great grandfather, or them being a child of the grandparents with something else going on farther back?
Hi Clare,
To get a result in the AYPR tool, the parents have to be related. It can’t be any further generations back than that. The AYPR predictor suggests something like the mother’s half-brother, uncle, or nephew being the father. How many segments are shared for those matches you listed? Which side are the uncle and aunt on? Which grandparent are the maternal aunt/uncle on (maternal paternal or maternal maternal)? Which side is the half-sister on?
Hi, so if I’m understanding correctly, then the total cm (not multiplied by 4) of 245.3 would be 1st cousin? It’s too small for half brother from what I’m reading I think. Largest segment 39.3 & total 245.3
Fascinating but confusing.
Yes, 1st cousin seems to be much more probable than the other options, especially since there’s no generational difference. However, the half-brother probability isn’t so so low that it could be ignored. Are the descendants of the potential 1st cousin who could have their DNA tested?
Hi there! I’m working on this for my cousin. We recently discovered her parents are related. Her results on the GED Match Are Your Parents Related tool (via her Ancestry DNA) show
Largest segment = 61.3 cM
Total of segments > 7 cM = 631.2 cM
What do you think this indicates as far as how her parents were related? I’m worried they might have been siblings.
Hello,
How many segments is that comparison? This page shows that the most likely scenario is that their father was their mother’s half-brother, grandfather, or grandson: https://dna-sci.com/tools/aypr-cim/
But I can get you something better if you have the number of segments.
Thank you for your reply! They share large segments on all but Chr 5,7, and 19. The largest segments are from Chr 18 or 21. I’m not entirely sure what I’m looking at. Thank you so much for your help.
What I mean is the total count of the segments. It should say somewhere on the page. Otherwise, you can count all of the rows where they show you the chromosome and segment positions.