Do you trust 23andme's Ancestry Composition or GEDmatch calculators more?

[Aquilifer]

What I want to find, and have not yet been able to do so, is a finer breakdown of the regions of North Sea, Atlantic, and Baltic. Those are the areas where the Germanic tribes held sway: Norse, Anglo-Saxon, Norman, Franks, Vandals, etc. Does anyone know how to get a finer breakdown, and why there's such a discrepancy between 23andMe and GEDmatch?

I'm no expert, but it could probably be broken down as such:

Atlantic=NW Europe
North Sea=Scandinavia
Baltic=NE Europe

[Thorbjorn]

I'm no expert, but it could probably be broken down as such:

Atlantic=NW Europe
North Sea=Scandinavia
Baltic=NE Europe

Thanks, That makes sense. I haven't been on the site for a while and didn't see this until now.

[Dorkymon]

It looks like the "typical" southern Italian is indeed descended from peoples who migrated from northern Europe, hence the high number of fair-skinned, light-haired Italians and Sicilians.

This should be the most deluded deduction I had read this month.

[jfttrh44]

Some people say that 23andme predicts ancestry from the last 500 years, and that it is therefore more reliable than GEDmatch.

I don't really agree because I've noticed very peculiar things happen with the 23andme calculator. I've seen families where one parent is Sicilian and the other is Irish. The Sicilian parent scores 15% Middle Eastern, while the child scores 0%. I've yet to see a half North European, half SE European (Cretan, Sicilian, Greek islander) score significant Middle Eastern even though full members of said groups score a significant amount.

Likewise, I suspect 23andme underestimates admixture when it is small. I have seen that in people with under 10% of African, the African is greatly underestimated on 23andme.

What do others think? I think due to its algorithms, 23andme ends up giving misleading results, but it is good for telling if a given ancestral component exists... just not necessarily the amounts.

The thing about the "500 years" is absolutely rubbish. I am from Spain, all my ancestors (I did my family tree until 1500) are fully Spaniards, and on 23andme and on gedmatch, 99% of my matches have non-spanish surnames. I practically have matches from many places in Europe except on Spain, and I am fully Spaniard for the last 500 years.

This means that the ancestry is older, the matches are older, and that very few Spaniards have tested on gedmatch. But my matches are much older than those 500 years, probably 1000-2000 years older.

[ArmandoR1b]

The thing about the "500 years" is absolutely rubbish. I am from Spain, all my ancestors (I did my family tree until 1500) are fully Spaniards, and on 23andme and on gedmatch, 99% of my matches have non-spanish surnames. I practically have matches from many places in Europe except on Spain, and I am fully Spaniard for the last 500 years.

This means that the ancestry is older, the matches are older, and that very few Spaniards have tested on gedmatch. But my matches are much older than those 500 years, probably 1000-2000 years older.

I agree that the autosomal DNA in Ancestry Composition at 23andme, which is what the 500 years old comment is about, is older than 500 years because it takes thousands of years, or extreme endogamy, for the autosomal DNA to become identifiable as a separate component and for it to also be very widespread. Iberians, from all over Iberia, and Latin Americans, from all over Latin America, get a very high amount of Iberian DNA but it is very low outside those populations. That in itself shows that it is more than 500 years old.

What 23andme is really saying about the 500 years old DNA is that is what your ancestors from 500 years ago had in their Ancestry Composition. At least the ones that you inherited the autosomal DNA from.

[jfttrh44]

What 23andme is really saying about the 500 years old DNA is that is what your ancestors from 500 years ago had in their Ancestry Composition. At least the ones that you inherited the autosomal DNA from.

I still don´t get what you say about this. So, if you have a more recent ancestor (from a very different ethnicity: for example someone from Finland), it would not appear because it will not affect the total?

So, in fact, all of these tools are always for older ancestry and never for newer (less than 500 years). And what happens with the people from America? All of them are mixed in the last 500 years, inside their race, and outside also.

[E_M81_I3A]

23andme compares your DNA to modern populations and not to the ancient components that made up these modern populations while most of GedMatch calculators compare your DNA to ancient components instead of modern populations.

For example, some North Africans get 100 % North African ancestry at 23andme which is correct, but it does not say anything about ancient SSA ancestry because it is included in the North African modern populations. Same for some Iberians who get 100% Iberian at 23andme which is correct, but in the same manner it does not say anything about ancient Maghrebi ancestry because it is included in the Iberians modern populations.

When they use GedMatch calculators, North Africans will generally get 15-25% SSA and Iberians will get 5-15% Maghrebi ancestry as ancient components that make up modern populations used by 23andme are here isolated.

So both 23andme and Gedmatch calculators are useful, it just depends on what we want to know.

[ArmandoR1b]

Same for some Iberians who get 100% Iberian at 23andme which is correct, but in the same manner it does not say anything about ancient Maghrebi ancestry because it is included in the Iberians modern populations.

It is extremely uncommon for an Iberian to get 100% Iberian at 23andme and most have a small amount of SSA or MENA along with small amounts of Italian and northern European at 23andme.

When they use GedMatch calculators, North Africans will generally get 15-25% SSA and Iberians will get 5-15% Maghrebi ancestry as ancient components that make up modern populations used by 23andme are here isolated.

That of course depends on the person and the Gedmatch calculator. The Spaniards that I have seen results for don't get Maghrebi at Gedmatch although there is almost no doubt that they have some Maghrebi in their ancestry. Which calculator are you using that shows Maghrebi in Iberians?

[Kurd]

23andMe's speculative mode greatly overestimates major components, and underestimates minor components. This is due to their methodology of snipping the genome into 100 SNP segments to compare against the limited references they have. So for example, if 60% of the the segment indicates Middle Eastern, and 40% indicates S Asian, that segment is assigned 100% Middle Eastern. In effect 40% of the segment, which is S Asian is ignored, and the whole segment is assigned Middle-Eastern.

Also, their methodology includes segment smoothing, which means if there are chunks of minor components in a segment, they are ignored.

That is how Iranians and W Asians turn out 98-100% Middle Eastern, and folks in neighboring Pakistan turn out 98-100% S Asian in speculative mode.

This naturally is unrealistic and uninformative, because you don't need a test to tell you that. Conservative mode is better with regards to inflation of major components and underestimation of minor components, but the trouble here is that people get 5-70% unassigned. This is where your minor components are hidden.

The above translates to 23andMe being useless for figuring out your minor components to any degree of accuracy

[E_M81_I3A]

The Spaniards that I have seen results for don't get Maghrebi at Gedmatch although there is almost no doubt that they have some Maghrebi in their ancestry. Which calculator are you using that shows Maghrebi in Iberians?

Some calculators have a North african component like Dodecad 12b, MDLP 23... Whenever there is a North african component then almost all Iberians get 5-15% of it. If there is no North african component then they get 1-4% SSA which is generally a signal of more important North African ancestry.

For example, a Galician's Dodecad 12b results (7% NAF and 3% SSA):



and a Portuguese (7% NAF and 1.5% SSA)




So far, I have not seen any Iberians, at least Western Iberians, at GedMatch without North african and/or SSA ancestry, but I am sure there are some in Eastern part of Iberia. Which region of Iberia is your ancestry from? have you tried Dodecad 12b for example ?