It is the nucleus that contains DNA and controls the functions of the cells
Since the means of reproduction have changed, the population of peacocks would probably start losing their pretty feather colors due to the fact that over time females would be mating with the containing the other trait (and possibly not the pretty feathers). This would then produce offspring with ugly colors but also with the desired trait. This would continue on and on until those with the desired trait outnumbered or possibly extinguished the now unnecessary vibrant feather colors.
