View Full Version : Orcadian accuracy in Gedmatch calculators?

06-13-2019, 04:34 PM
I understand gedmatch calculators could stand to be updated, but how accurate are they for discerning between Orcadian vs broadly Scottish, or Irish for that matter?

I ask b/c my ancestry has some Scottish with traces of Irish interlaced, but that line dead ended at a grave in north/northeastern Scotland after tracking a long history in the US.

Although I don't seem to have inherited much DNA from this line, when it does show up in gedmatch, it's nearly always listed as Orcadian. Which causes me to wonder, since the only ancestry found in Scotland wasn't too far off, how suggestive is this in locking down northern Scotland descent?

I'm an interested novice hoping to understand more of how everything works. My family tree is pretty well documented by someone with more experience, and this is just a blank spot I've been curious about.

06-13-2019, 04:58 PM
The amount of Scottish ancestry you may have (both Orcadian and peninsular Scottish), alongside the rest of your known ancestry, will determine how accurate the GEDmatch outputs you're seeing are.

Having said that, the extremely high degree of overall similarity observed between Orcadians and other Scots makes an attempt to distinguish between the two through autosome-wide analyses reliant on component formation next to impossible. They appear identical, for all intents and purposes, in Davidski's G25 data (both ~73% Corded Ware, ~27% Neolithic Scottish; overall proximity fit of ~0.6, which is intra-family-like closeness):

Sample Details Fit Map Corded Ware CZE Scotland N WHG
1 Orcadian:Average 2.162 Open Map 73.2 26.8 0
2 Scottish:Average 2.383 Open Map 73.6 26.4 0

Expanding the above to include the Irish and Welsh yields a similar outcome:

Sample Details Fit Map Corded Ware CZE FRA MN WHG
1 Irish:Average 2.6034 Open Map 75.8 24.2 0
2 Orcadian:Average 2.2151 Open Map 75.6 24.4 0
3 Scottish:Average 2.3828 Open Map 75.8 24.2 0
4 Welsh:Average 2.5059 Open Map 75.2 24.8 0

Whether these populations are actually approximately three-quarters Corded Ware and one-quarter additional Early European Farmer is another discussion - Their overall near-congruity is the focus of the comparison here.

IMO, you're best off looking at IBD segment analysis for yourself (and preferably the parent of yours who has the Scottish/?Orcadian ancestry) to try and narrow the signal down.

06-13-2019, 05:44 PM
Me scaled

sample": "Custom:AGUser_firemonkey",
"fit": 2.7609,
"Corded_Ware_CZE": 73.6,
"Scotland_N": 25.6,
"WHG": 0.8,

Me unscaled

"sample": "Custom:AGUser_firemonkey",
"fit": 1.8133,
"Corded_Ware_CZE": 80.2,
"Scotland_N": 19.8,
"WHG": 0,