Dramatic regional variations for suites of biological traits no longer exist in some populations because of:​

A) ​genetic drift
B) ​gene flow
C) ​mutation
D) ​speciation

Gene flow refers to the exchange of genes between populations, which can reduce or eliminate regional variations in biological traits. This could occur if individuals from one population migrate to another population and interbreed, leading to the mixing of genetic traits. Genetic drift, mutation, and speciation may also play a role in shaping biological diversity, but they do not necessarily explain the elimination of regional variations in biological traits as effectively as gene flow.