The population of the United States has been characterized
as a cultural melting pot, with over 500 ancestries
reporting in the 2000 Census [14]. However, for forensic
purposes U.S. populations are typically categorized as
African–American, Caucasian (European–American), Hispanic,
Asian–American, and Native-American (we note
that the U.S. census considers the ‘‘Hispanic’’ category
separate from other ethnic groups because Hispanics are a
heterogeneous group with multiple origins, see Section 4).
Genetic studies indicate significant differentiation among
these ethnic groups; a major outstanding question concerns
the level of population structure within ethnic groups [15],
especially for the Y chromosome. The extent to which we
expect genetic heterogeneity among populations within an
ethnic group in the U.S. depends mainly on four factors:
levels of subdivision in ancestral source populations (e.g.,
Africa, Europe, etc.), the extent of non-randommigration to
the U.S., migration rates among geographic regions after
arrival in the U.S., and the degree to which inter-ethnic
admixture varies regionally

LINK