Need Help!
You and 19 friends build a raft, sail to a deserted island, and start a new population, totally isolated from the world. Two of your friends carry (that is, are heterozygous for) the recessive cf allele, which in homozygotes causes cystic fibrosis. Assuming that the frequency of this allele does not change as the population grows, what will be the incidence (in percent) of cystic fibrosis on your island?

Question

Need Help! 
You and 19 friends build a raft, sail to a deserted island, and start a new population, totally isolated from the world. Two of your friends carry (that is, are heterozygous for) the recessive cf allele, which in homozygotes causes cystic fibrosis.  Assuming that the frequency of this allele does not change as the population grows, what will be the incidence (in percent) of cystic fibrosis on your island?