Ancestry DNA Test

dubhthach wrote: »

Well you have to remember that the estimates are basically 'software calculators' that use 'reference samples' to infer percentages. In such a case the model is only as good as the data that is fed into it.

so to take an extreme case, if their calculator only had three sample populations:
1. Congolese
2. Japanese
3. Swedish

Then in such a scenario an Irish person data fed into it would probably show up as 100% 'Swedish'.

So obviously the first step is to try and build a sampleset from every and any possible population group.

Of course if you have small samplesets you run into another "issue", in that neighbouring populations tend to be more closely related to each other then distant ones. So for example your average Irish person and average Swede will have shared more recent common ancestors with each other then either would with someone with origins in say Mongolia. Likewise someone from Mongolia will have more recent shared ancestry with say someone from Northern China or Korea then they do with either Swede or Irish person.

In such a case you need to have relatively large samplesets for each population. This allows you to
(a) generate a better picture of what average person in a population looks like when it comes to genetic variation
(b) push certain components backwards in time to more ancient admixture

b. above is possibly what happened with Scandinavian bit in your case. You have to remember that tests such as Ancestry been autosomal are really looking for matches in last 200 years.

Now there's some research that points that modern Irish people appear to have a certain level of 'Norse' admixture in them. RCSI proposed this in their paper on the 'Irish DNA Atlas'. I'm not so sure on their methodolgy for number of reasons:
1. They use only modern sample populations from both Ireland and Europe
2. They don't have any ancient DNA from pre-viking Early christian period -- as a result no baseline for level of admixture flow
3. They have no ancient DNA from Scandinavia to provide a baseline for 'Viking period' population structure. (eg. Nordic Iron age/Early Viking period timeline)



Anyways to go back linguistic point of view it's worth pointing out that both speakers of Germanic languages (eg. English, Dutch, German, Swedish, Norwegian, Danish etc.) and Celtic language (Irish, Scottish Gáidhlig, Welsh, Breton etc.) would have shared a common language on order of 4-5k years ago in Proto-Indo-european.

4-5k years isn't a huge period for genetic differenation to build up. In comparison the spilt say between Western Europeans and East Asians is more on order of 30-45k years ago. (leaving aside that there have been levels of admixture back and forth since on smaller scale)