Question

Mathephobia is a dreaded (but hypothetical) recessive condition that causes students to go into convulsions whenever they see formulas in biology class. D is the normal allele, d is the mathephobia allele.

DD and Dd individuals are normal

dd individuals are Mathephobic

In a class of 100 biology students, 32 had convulsions during their first population genetics lecture. Assume that students are a representative sample of a population at Hardy-Weinberg equilibrium.

a) What is the frequency of the mathephobia (d) allele in this population?

b) How many students in this class are homozygous dominant (DD) and heterozygous (Dd) for this condition?

The trauma induced by a second genetics lecture caused 75% of the students with the mathephobia to spontaneously combust and disappear.

c) What is the frequency of each allele in the surviving population of genetics students?

d) What are the frequencies of each genotype and phenotype?

Answer 1

a).

Frequency of convulsion trait = dd=32/100 = 0.32

Frequency of convulsion allele = d = 0.57

As p+q=1

The frequency of normal allele = D = 1-0.57= 0.43

b).

Frequency of DD = 0.43 * 0.43= 0.19

DD individuals = 0.19 * 100 = 19

Frequency of Dd = 2* 0.43 * 0.57= 0.49

DD individuals = 0.49 * 100 = 49

c).

75% is out of 32 students disappear = .75 * 32 = 24

Remaining mathephobia students = 32-24= 8

Frequency of dd= 8/(8+68) = 0.11

Frequency of allele, d = 0.33

Frequency of allele, D = 0.67

d).

Frequency of genotype, DD= 0.67 * 0.67 = 0.45

Frequency of genotype, Dd= 2* 0.67 * 0.33 = 0.44

Frequencyof genotype dd= 0.11

Frequency of normal phenotype = DD + Dd = 0.45 + 0.44= 0.89

Frequency of mathephobia phenotype = dd = 0.11