Question

1) In Lab, we tested everyone’s phenotype using PTC paper.

What are the two possible phenotypes?

What genotype(s) are associated with each phenotype?

2) In our hypothetical population of 24 students, we have 17 tasters and 7 non-tasters.

Using the Hardy Weinberg equilibrium equation p2 + 2pq + q2 = 1

Applying this equation to the gene involved in tasting PTC:

Which genotype is represented by the frequency p2?

Which genotype is represented by the frequency 2pq?

Which genotype is represented by the frequency q2?

Calculate the frequency for q2. To do this use the number of non-tasters divided by the total number of students. This will give you the genotype frequency for our lab population:

What value did you get for q2?

Now, use that frequency to calculate the value for q. q is the allele frequency for the recessive - a - allele in our lab population. Taking the square root of your q2 value will give you q.

What value did you get for q?

For any gene locus with two alleles, the following equation is true of the allele frequencies:

p + q = 1

Use this equation to identify p, which is the allele frequency for the A allele in our class population.

Use your values for p and q to calculation the genotype frequencies for p2 and 2pq.

What value did you get for p2?

What value did you get for 2pq?

Answer 1

ANSWER 1 :-

1. PTC stands for Phenylthiocarbamide. This is a chemical which is used to identify whether an individual is a 'taster' or a 'non-taster' which are the two phenotypes associated with tasting principle.
2. This individual who are able to taste PTC are called as 'Tasters' and are represented by the genotype 'TT' or 'Tt' whereas the individuals who are not able to taste 'PTC' are called as 'Non-taster' and are represented by the genotype 'tt'.
3. The chemical is bitter to taste and only the individuals who are autosomal recessive would tend to show the non-taster potential.

ANSWER 2 :-

The genotype 'TT' is represented by the frequency p2

The genotype 'Tt' is represented by the frequency 2pq

The genotype 'tt' is represented by the frequency q2

Total number of non-taster is 7 individuals in total group of 24 individuals.

So, q2 = (7/24) = 0.29

q = √q2 = √(0.29) = 0.54

P = 1 - q = 1 - 0.54 = 0.46

p2 = (0.46)2 = 0.21

2pq = 2 × (0.46) × (0.54) =0.50

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