Question

Suppose a population is carrying a condition controlled by two alleles: R (dominant) and r (recessive). Only homozygous individuals that have two copies of the recessive allele have the condition. If the r allele is found in 15 percent of the population, what's the frequency of the RR genotype? A. 72.25 percent B. 12.75 percent C. 25.5 percent D. 2.25 percent

Answer 1

The answer is; A.

If r allele is found in 15% of the population, then the frequency of the allele is;

r = 15/100 = 0.15

Remember the equaition p + q = 1

Therefore; R + r = 1; R + 0.15 = 1; R = 1-0.15 = 0.85

RR = 0.85*0.85 = 0.7225

In percentage = 0.7225*100 = 72.25

Answer 2

To calculate this, you have to do the following. 

If you know someone thta the r allele has a 15% occurence in the population, then you know that the R allele has a 75% occurence in the population. 

Knowing this, you can then just multiply all the possible combinations to see what are the posibilities of finding an indviidual with two dominant alleles. In this case, it's 72,5%.