[yumraj]

Disclaimer, I'll not a geneticist. And I've seen, read, or come across various studies supporting opposite viewpoints. Given that, it is non trivial to decide what is the ultimate truth and the truth we decide to pick depends on our own biases. And I don't think this question is settled and may never be settled.

My personal take, for what it's worth, there was no mass scale migration and North and South Indians are the same people. However, there was a lot on influx/migrations/invasions in North from rest of Asia and farther, which led to genetic mixing and the deviations that we see.