Karma or Genetics, which one drives?

Karma is the more abstract accumulation. 

Then comes genetics.

Karma can dominate genetics ----or---- Genetics can dominate karma.

Once a person lives long enough and accumulates immense amounts of karma,

That starts to play a bigger role.
For animals their genetics dominates much more than their karma.
For a human with immense amount of karma, that plays a bigger role and acts as the driver of the genetics-forces.