3. (2) After graduation, you and 19 of your closest friends (lets say 10 males a

Question

3. (2) After graduation, you and 19 of your closest friends (lets say 10 males and 10 females including you) charter a plane to go on a round-the-world tour. Unfortunately, your plane crashes-but you all land (safely!) on a deserted island. No one finds you and you start a new population totally isolated from the rest of the world. If two of the individuals in the group carry (are heterozygous for) the recessive cystic fibrosis allele (c) and assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island? (I'm asking you to find the genotypic frequency for the cystic fibrosis condition,

Explanation / Answer

Assuming C is the dominant allele and c is the recessive allele (cystic fibrosis causing allele)

If there are 20 students means, there are 40 alleles (either C or c alleles).

Only two of them are heterzygous (means Cc). So, the number of c alleles in the population is 2 out of 40 and the remaining 38 are C alleles.

Now we caluclate the frequency of the recessive allele will be 2/40. i.e. q = 0.05.

cystic fibrosis incidence occurs only if the two alleles are c (i.e, cc). Only homozygous individuals are affected.

In hardy-weinberg equation q2 represents genotypic frequency.

We know the value of q=0.05 and q2= 0.0025

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