Really? You're asking a bunch of people on a chat forum a complex question about DNA and expect a response that will give you "the answer?" Good luck with that!
Additionally, please note in your question, you have asked about one particular allele--you wrote "high frequency of THIS allele"--so ... duh... for us to even START to answer it, we would have to know what the "THIS allele" is.
Therefore, to give you the best answer possible... I'd have to say Blue hit it on the head. Aliens.