READERS’ LETTERS
Many thanks to Christene Hoffert for e-mailing about her experiences with ethnicity estimates.
Hi, first of all, my three ethnicity estimates from Ancestry, Familytreedna and Living DNA have me 100% European.
Ancestry ethnicity does not match my genealogy research back to the mid 1700s. With 36% Scotland and no shared matches, it is a mystery as I have one, possibly two, 3x greatgrandparents who were born in Scotland around 1760s, which do not equal anywhere near 36%. Many of my ancestors did, however, come from Cumbria and Northumbria but were in northern England in the 1750s.
Living DNA gives 32% from Cumbria and 20% East Anglia, both of which match my genealogy as well as segment matches on DNA. FTDNA identifies 24% Ireland which may be a little high, but my 2x greatgrandmother was from there and I have a lot of DNA matches with that ancestral line.
If I had a brick wall in this time frame, the ethnicity estimate would be useless for Ancestry.
Another problem with Ancestry is on the segment matches that I find on Gedmatch which are supposedly from Ancestry and are not found. The one I did find with a third cousin missed a significant segment with the DNA match. I know that segment size can be different for different DNA websites, but missing a segment altogether causes me to suspect as to what other results are incorrect. Thank you for letting me share this.
Christene
Karen writes: In terms of the ethnicity estimates:
Depending on the companies’ reference panels, you will see differences within your breakdowns. Livingdna have really focused on dividing the UK into areas within their reference panels, so they are known to offer a more distinct breakdown. Ancestry is less sensitive to specific areas in the UK, tending to breakdown in regions for the ethnicity reading. They then use communities which look at how your matches are clustered which ‘may’ indicate where your family were in the last few hundred years. All the companies are looking at ethnicity from 500-1,000 years back, with communities within the last few hundred.
At the moment your ethnicity will be correct at a continental level, but the rest is educated guestimates. Indeed, if you look at the ethnicity estimates on Ancestry they will actually give you a range. In the last few years my father has gone from 45% Scandinavian to 0% according to
his estimate. Missing chromosomes:
Ancestry have developed an algorithm called Timber that downweights segments of DNA which it considers are common to vast groups of the population and are therefore genealogically unhelpful. This is unique to Ancestry but their cm amount is probably the most accurate because of this. Your missing segment is most likely one of the smaller segments and some parts of the others. Your match is valid (which you of course know from research) but Ancestry questions whether all the DNA shared is actually from those common ancestors. Some of the DNA, it believes, comes from Identical by State (IBS) rather than Identical by Descent (IBD) and endeavours to downweight it to assist with more accurate matching. In other words they feel part is from the common ancestor, the rest IBS. Even with this, a proportion of matches will be false due to IBS. I have tested on Ancestry and so have both my parents but I have a match that neither of them have (even as a combined smaller amount). Since DNA can only come from my parents, this match must be false.
Of course, if you have endogamy Ancestry could remove cm which is actually valid so it does depend on certain circumstances. Those smaller matches on Gedmatch may not appear on Ancestry because Timber has downweighed their significance.