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After graduation, 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(heterozygotes) the recessive allele c, which causes cystic fibrosis in homozygotes.

Assuming that the frequency of this allele does not change as the poulation grows, what will be the instance of cystic fibrosis on the island?

I'm thinking 1/4...but not sure..any ideas?

You neglect to give the gender of the 20 people. If they are all males or all females, there is no incidence, because they cannot reproduce.

In the first generation, there will also be no chance for being homozygous, if both of the carriers are of the same gender.

The male/female ratio is very important in determining the number of pairings available. What if there are only 2 males and 18 females, with the males being the carriers? What if two of the females in this ratio were the carriers?

I'm thinking that we need more information.

This is probably making the situation more confusing, but I hope it helps. Thanks for asking.

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