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Post date: Nov 28, 2015 8:17:53 PM
AncestryDNA has recently added a nearly hidden new feature. If you click on the "i" next to the "confidence" estimate on your DNA match, AncestryDNA now shows the "amount of shared DNA" that you have with that match (see above). What they are showing is the length of the segments, measured in centimorgans (cM), and how many separate segments this length is divided between. This can provide you with an estimated average length of matching segments, but in general, it does little other than to provide a tiny bit of insight into the basis for the confidence rating.
Unfortunately, I have been unable to obtain an answer from AncestryDNA as to the minimum threshold that they use to determine a matching segment. It does, however, appear that they use a length of at least 3 cM as the minimum segment length, but I don't know the number of SNPs that they require. It also looks like, in order to be considered to be a DNA match, AncestryDNA requires either:
- A single segment of 5 cM; or,
- At least 3 segments of 3 cM (very short segments).
These numbers are based on empirical evidence, and were not provided by AncestryDNA.
What would be far more relevant would be to tell us what the length of the longest matching segment is, and to show us precisely which segments (start and stop loci by chromosome) that are matching. These are features that are currently available on FTDNA and on 23andMe.
Ancestry have been promising that "exciting new features" are on the way at AncestryDNA. Hopefully, these will be some of the new features that we can look forward to seeing at AncestryDNA.
Get the most value out of your DNA test with the help of an experienced professional. Contact Ancestors & Cousins today.
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