Question

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1. In a population of rats, the frequency of gene b (for white coat) is known to be 0.6. What proportion of the next generation should have brown coats? [ Answer: 64% ] Suppose you were to pick one of the brown-coated offspring at random. What is the probability that this rat would be homozygous for the B allele? [ Answer: 16/64 or 0.25 ] 2. In snapdragons, Red flowered and white flowered plants are both homozygous (RR and rr respectively). The heterozygous individuals (Rr) have pink flowers. In a patch of snapdragons, 60% of the plants have red flowers. What are the frequencies of the two genes? What proportion of the plants would be expected to have pink flowers? White flowers? [Answers: R frequency is 0.7746; r frequency is 0.2254. So, 34.9% should have pink flowers (2 x .7746 x.2254) x 100. The remaining 5.1% should have white flowers.]

Answer 1

Answer:

1).
Frequency of recessive allele = b = 0.6

Frequency of dominant allele = B = 1-0.6 = 0.4

Proportion of brown = PP + Pp = 0.4*0.4 + 2*0.6*0.4 = 0.64 = 64%

Proportion of homozygous brown = PP = 0.4*0.4 / 0.64 = 16/64 = 0.25

2). Frequency of red flowers = RR = 60% = 0.6

Frequency of red allele = R = SQRT of 0.6 = 0.7746

Frequency of white allele = r = 1 – 0.7746 = 0.2254

Proporytion of Pink flower = Rr= 2*0.7746 * 0.2254 = 0.349 = 34.9%

Proportion of white flowers = rr = 100 – (60% - 34.9% ) = 5.1%