The relationship between the two don't have many similarities, both populations are always looking out for ones who can hurt or kill them and the other is looking out for which is the easiest to hunt. Since predators kill the prey, the predator population would be larger than the prey population.
I believe the answer is vaccines
Assuming that the disorder is recessive, the phenotype for someone carrying the disorder would be Bb. Someone who doesn't have the disorder would be BB. Bb x BB = BB, BB, Bb, Bb. 50% would not have the disorder and 50% would be carriers.