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View Full Version : Ancestry Composition vs. IBD Segments



J Man
12-26-2014, 09:12 PM
This topic is about the segments and percentages that people have on Ancestry Composition vs. IBD segments. On Ancestry Composition at 23andme I have seen individuals of pure French and Dutch ancestry scoring around 30% or so in the British and Irish component. So of their chromosomes are comprised of what looks to be almost an entire half or so of the British and Irish component. Now in comparing these exampled to actual IBD segment matches I do not really think they are the same. For example I share an IBD segment with my great uncle who is from Ireland that is around 93 cM in size. A person of 100% French or Dutch ancestry and who's ancestors lived in France or the Netherlands for the last 3 generations or so should not be able to share an IBD segment that is as large as the one I mentioned above that I share with my uncle with a person of 100% Irish or British Isles ancestry correct? Even if they score around 30% or so British and Irish on Ancestry Composition and have what look to be some very large chromosome segments identified as British and Irish? I hope this all makes sense.