Hardy-Weinberg Tutorial

This tutorial is designed to try and help you understand the basics of Hardy-Weinberg Equilibrium. Please work through the entire tutorial.

Question 1

Hardy-Weinberg equilibrium makes several assumptions. Which two of the those listed below are not assumptions which must be met for a population to reach Hardy-Weinberg Equilibrium?

(a)Sexaul Reproduction
(b) Non-overlapping Generations
(c) Random Mating
(d) Natural Selection occurs
(e) Population size is small
(f) All of the above are assumptions of Hardy-Weinberg Equilibrium.

Question 2

Which of the equations below is Hardy-Weinberg Equilibrium based on?

(a) p + pq + q = 1

(b) p + 2pq + q = 1

(d) p2 + 2pq +q2 = 1

(e) p2 + 2p2q2 +q2 = 1

Question 3

When a population is in Hardy-Weinberg Equilibrium,

(a) allele frequencies decline at a steady rate

(b) allele frequencies stay the same

(d) genotype frequencies decline at a steady rate

(e) genotype frequencies stay the same

(f) genotype frequencies increase at a steady rate

Question 4

Assuming that the rest of the Hardy -Weinberg assumptions are met, how many generations of random mating are required to bring a population into Hardy-Weinberg Equilibrium?

(a) 0 - random mating never brings a population into Hardy-Weinberg Equilibrium

(b) 1

(d) 100

Question 5

Suppose that the deformed frogs that have made the press recently are the result of a parasite infection and that in a nearby Indiana pond, we know that there is a parasite resistance allele in the population. The allele has a frequency of 20% and is a dominant allele. What percentage of the population is predicted to be resistant to the parasite should it be introduced into the pond?
a. 20%
b. 4%
c. 36%
d. 64%
e. 80%
f. 32%

Question 6

What if the allele had a frequency of 20%; however, we were wrong, the resistant allele is a recessive allele not a dominant allele. What percentage of the population is predicted to be resistant to the parasite should it be introduced into the pond?

a. 20%
b. 4%
c. 36%
d. 96%
e. 80%
f. 32%

Question 7

If the resistant allele had a frequency of 20% and was recessive allele, what percentage of the population would be susceptible to the parasite but still carry an allele for resistance?
a. 20%
b. 4%
c. 36%
d. 96%
e. 80%
f. 32%

Question 8

Red foxes have three different types of coat color, red, cross, and black/silver (see the image) which is controlled by two loci each with two alleles. We will only be concerned with the "A" locus here.

Suppose you went to YellowstoneNational Park and counted how many foxes you saw of each color-phase. You talk with one of the Ranger-naturalists at the end of the trip, telling her that you saw 58 red-phase, 32 cross-phase, and 10 black/silver-phase foxes. The naturalist wants to know more about the these foxes so she asks you a series of questions.

What was the frequency of the "A" allele?

(a) 7% / (b) 10% / (c) 26%
(d) 38% / (e) 55% / (f) 58%
(g) 74%

Question 9

What was the frequency of the "a" allele?

(a) 7% / (b) 10% / (c) 26%
(d) 38% / (e) 55% / (f) 58%
(g) 74%

Question 10
Red foxes have three different types of coat color, red, cross, and black/silver (see the image) which is controlled by two loci each with two alleles. We will only be concerned with the "A" locus here.

Assuming that the population mates randomly, what frequency do you expect the "A" allele to be at in the next generation?

(a) 7% / (b) 10% / (c) 26%
(d) 38% / (e) 55% / (f) 58%
(g) 74%

Answers

Question 1 You said that (a)Population size is small was not an assumption of Hardy-Weinberg Equilibrium.
YES! Hardy-Weinberg Equilibrium assumes that population size is very large.

Question 2

You said that (d) p2 + 2pq +q2 = 1is the equation associated with Hardy-Weinberg Equilibrium.
Yes, this is the equation that is associated with Hardy-Weinberg Equilibrium. In this equation p2 represents the frequency of individuals who are homozygous for one allle, 2pq is the frequency of heterozygous individuals, and q2 is the frequency of individuals who are homozygous for the other allele.
You can see how the equation works by looking at the table below.

p / q
p / p2 / pq
q / qp = pq / q2

Adding the cells of the table together then provides you with, p2 + pq + pq + q2 = p2 + 2pq + q2.

Question 3

You said that (b) allele frequencies stay the same when in Hardy-Weinberg Equilibrium.
Yes! In Hardy-Weinberg Equilibrium allele frequencies should not be changing. Equilibrium implies a steady state, one that is unchanging, so if allele frequencies are changing the system can't be at equilibrium.

Question 4

You said that (b) 1generation of random mating will bring a population into Hardy-Weinberg Equilibrium.

Question 5

YES! One generation of random mating is sufficient to bring a population into Hardy-Weinberg Equilibrium.

You said that the expected frequency of resistant frogs is (c) 36%.
YES! Because the allele is dominant you know that homozygous and heterozygous individuals for the "R" allele are resistant.
we are given that p = 0.20, therefore q = 0.80 and we can assign frequencies to the 3 possible genotypes at this locus:

RR / Rr / rr
p2 / 2pq / q2
(0.2)2 / 2(0.2*0.8) / (0.8)2
0.04 / 0.32 / 0.64

Because both RR and Rr individuals are phenotypically resistant to the parasite (i.e., R is dominant to r), the percentage of resistant individuals is .04 + .32 = .36 or 36% and alternative c is correct.

Question 6

You said that the expected frequency of resistant frogs is (b) 4%.
YES! Since the allele is recessive only individuals who are homozygous for the "r" allele will be resistant.

we are given that p = 0.80, therefore q = 0.20 and we can assign frequencies to the 3 possible genotypes at this locus:

RR / Rr / rr
p2 / 2pq / q2
(0.8)2 / 2(0.2*0.8) / (0.2)2
0.64 / 0.32 / 0.04

Question 7

You said that the expected frequency of resistant frogs is (e) 32%.
YES! Only the heterozygous individuals are susceptable but still carry an allele for resistance.
we are given that p = 0.80, therefore q = 0.20 and we can assign frequencies to the 3 possible genotypes at this locus:

RR / Rr / rr
p2 / 2pq / q2
(0.8)2 / 2(0.2*0.8) / (0.2)2
0.64 / 0.32 / 0.04

Question 8

You said that the frequency of the "A" allele is (g) 74%.
YES! You must have remembered that to find the number of "A" alleles you count how many "A" alleles there are and then divide this by the total number of alleles in the system. {2 x 58 (from red-phase foxes) + 1 x 32 (from cross-phase foxes)}. There is a total of 100 foxes and since each fox has 2 alleles there is a total of 200 alleles in the system. So finally you have the number of "A" alleles = 148/200 = 0.74.

Question 9

You said that the frequency of the "a" allele is (c) 26%.
YES! Which one of the 2 different ways described below did you get to this answer?
There are two ways to figure out the frequency of the "a" allele. In the last question you said that the frequency of the "A" allele was 0.74 (or 74%). Since there are only 2 different types of alleles in the population and the total of those two frequencies must = 1, (p + q = 1), you can use the equation 1.0 - p = q.
or
Remember that to find the number of "a" alleles you should count how many "a" alleles there are and then divide this by the total number of alleles in the system. There are 10

black/silver-phase foxes each with 2 "a" alleles, and 32 cross-phase foxes each with 1 "a". So there are a total of 52 "a" allleles {2 x 10 (from red-phase foxes) + 1 x 32 (from cross-phase foxes)}. There is a total of 100 foxes and since each fox has 2 alleles there is a total of 200 alleles in the system. So finally you have the number of "A" alleles = 52/200 = 0.26.

Question 10

You said that the frequency of the "A" allele in the next generation would be (g) 74%.
YES! When the population mates at random the allele frequencies don't change between generations. That is specifically what is so special about Hardy-Weinberg Equilibrium, it allows you to know what the allele frequencies will be in the next generation, and from that the genotype frequencies