Previous studies showed that the floral color of a plant is controlled by a sing

Question

Previous studies showed that the floral color of a plant is controlled by a single gene B. The allele B is dominant over allele b. The dominant phenotype is blue color, while the recessive is white. In a field, out of 1,000 flowers surveyed, only 40 are white. Assuming Hardy-Weinberg equilibrium in this population, please answer Questions 20 to 21.

What is the allele frequency for the B allele? Ans = .80

What is the Rr genotype frequency in this population? Ans=.320

My exam is tomorrow and this is a practice question that he gave with the answer. I have NO IDEA HOW HE GOT THIS ANSWER. Please help me and explain this THOROUGHLY . I really need to do well in this course!

Please help me!

Explanation / Answer

HW Equilibrium says,

p+q =1, where p is allele frequency for B and q is allele frequency b, the sum must be equal to one. if you square the equation you get

p2+q2+2pq = 1, where p2 is the genotypic frequency of individuals with BB, q2 is the genotypic frequency of individual with bb and 2pq is the genotypic frequency of individuals with Bb

since 40 are white and white is the recessive trait, they must be bb, right, so the genotypic frequency for bb is 40/1000 (from the data)= 0.04.

Now this corresponds to q2 in Hardy Weinberg equilibrium, so q = 0.2(square root of 0.04),

since p +q must equal 1, p =0.8

now genotypic frequency for Bb is 2pq = 2 * 0.8*0.2 = 0.320

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