2n because when 2 gametes of n amount of DNA fertilise together they make an organism that is similar to its parents and have the total amount of DNA as 2n, just like parents.
Through reproduction. dark fur is a dominant trait and eventually if offspring of the one dark furred mouse reproduce enough, it will eventually spread to the whole population because it is a dominant gene and will overpower recessive genes of the other parent organism that the dominant mouse is reproducing with.
