People within an ethnic group are more genetically similar to others in their ethnic group than they are to an ethnic group from the opposite side of a globe.
Not true Genetic differences are just as great within ethinic groups as without
Wilkapedia
A 2000 study by Celera Genomics found that human DNA does not differ significantly across populations. Citizens of any village in the world, in Scotland or Tanzania, have 90 percent of the genetic variability humanity has to offer. Only .01 percent of genes account for a person's appearance.
[15] Biological adaptation plays a role in bodily features and skin type. According to Luigi Luca Cavalli-Sforza, "From a scientific point of view, the concept of race has failed to obtain any consensus; none is likely, given the gradual variation in existence.
Ethnicity and Nationality in Mixed Genetics
Dr. Orville Boyd Jenkins
Genetic heritage is different from our ethnicity. Ethnicity is developed or to some degree agreed upon by participants, and depends on the shared experiences and mutual acceptance. You see this in the groupings within one society, that at some level might be considered as one society, but in reality contains many ethnic groups. The native language of most groups of people in the US, for instance, is English.
But we will find distinctions at some level of society. Sometimes it is due to enforced distinction, which may be largely artificial, like the more obvious color distinctions that led to the creating of "race" as "color" in the US, forcibly separating the residents of African origin from those of European origin. Similar steps were taken against Asians and Eastern Europeans.
So the number of immigrants settling in the same community or the number of people of any similar culture living together, whether by their own choice of enforced by others, can lead to a distinction of class or caste that becomes one aspect of self-definition. These factors go into ethnic identity. Ethnicity is largely an interaction of Self-Identity with the attitude of others.