If you look at this Ancestry Article, you may find some clarity, if you are looking at Ancestry Ethnicity Estimates -
https://support.ancestry.com/s/artic...eference-Panel
but I think the other companies work on similar lines.
You will see that of the 44,703 people on the reference panel, 2095 are of long term Germanic background, while 1326 are from Britain and North Western Europe. 1411 are of Scottish background while just 480 are from Wales and 732 from Ireland.
I deduce from these figures, that if you have a proportion of DNA from, say, Welsh background, it will not show up unless you share DNA with some of the 480 on the reference panel.
Two of DNA profiles I manage have relatively high proportion Scottish ethnicity estimate (39%) but a very small Irish component (2%) Based on the family tree, showing about the same number of ancestral lines back to Scotland and Ireland, I would have expected the percentages to be very similar. The Welsh percentage is 4%. With only one 4xg grandparent from Wales but half a dozen from Ireland, this does not seem to make sense - except that the DNA profiles have Irish DNA roots which are not represented in the panel, but a proportion of the Welsh reference panel share DNA with our profiles.
Another DNA sample has a very high proportion of Scottish ethnicity (17%), despite no paper trail to Scotland, or people who moved from Scotland within the last 400 years. When i look closer at this estimate is says it could be 0% to 20%, which makes the 17% very misleading.
As the panel is changed and updated, I am sure the estimates will change. The earlier estimates for this sample were more correlated to the paper trail.
I am interested in finding about more about the reference panel - how they are chosen, are they regular Ancestry DNA samples, how often is the panel changed or updated, do they know they are on the reference panel?
Hope this might help in some small way
PS - this article might also help explain
https://www.wired.com/story/your-eth...think-it-does/
.