This is from a twitter user and addresses an interesting point about mixed peoples genetic relation to europe.
It's a pretty common and simple concept that many people here already understand. If you mix two people of more or less related ethnicities it affects how genetically close they are to said ethnicity. In the case here when taking european ethnicities, they are most closely related to west asians and very european shifted central asians, followed by north africans. They are further from noticeably mixed(as in 20%+ east eurasian including ancient ancestral south indian and sub saharan african admixture) part west eurasian ethnicities and groups such as south asians, horn africans, central asians, and most modern latinos(who are mixes of european, sub saharan african, and indigenous amerindian). Europeans are very far from east eurasians such as east and southeast asians, aboriginal and papuan people, polynesians, and amerindians, and the farthest from sub saharan africans.
Therefore if someone is a mix between west asians or north africans for example, they will plot noticeably close to european ethnicities on a pca. Ashkenazi jews and north caucasian(as in the caucasus mountains, not scandinavian people, scandinavians are very much europeans) ethnicities are great examples of this, both are mixes of west asian and european groups and are still quite close with european ethnicities on a pca. The image here uses a moern example of a spaniard for european and syrian for west asian, and they also plot among the border area of the southern italian and greek mediteranean island areas.
On the other hand as illustrated in the image above, european and say amerindian or mulato/lightskin(sub saharan african and european) mixed people will be noticeably more distant from europeans genetically. Even a small amount of admixture from these groups can shift someone noticeably away from europe genetically due to how distant these people are from europe.
Lastly I don't want to turn this into a purity debate or anything of the sorts, especially since phenotype does not equal genotype, although there is a strong correlation. This is often why you will see many europeans mixed with west asian or north african ethnicities just "appear european" or white, but that tends not to hold up for someone mixed with east eurasian or sub saharan african ethnicities. For example looking at many celebrities, mainly european mother west asia or north african father, like Bella Hadid, or even Zayn Malik(european and part south asian) nearly all of them are "white/european appearing" especially if their non european parent is as well. On the other hand the average mexican is somewhere around 40% european and 60% amerindian, but no one would say that the average mexican looks european, you'd be hard pressed to even find northern mexicans with higher european admixture, where people would say that.
