Biologist:__________________________
Hardy-Weinberg Lab
Materials: Teddy Grahams, calculator
Background
We have already determined that there is variation within a population. We have seen that individuals get their information or
instructions from their parents. We have also seen the composition of a population may change. You may want to use chapter 23 in
your textbook to help answer some of the questions.
1. In the lab today we will see two different versions of a trait. We call the versions phenotypes. Look at your bears and determine the
two phenotypes.
Procedures
Information: The bears with their arms up are aggressive and they are harder to hunt, the bears with their arms down are not
aggressive and they are easier to hunt. Predators prefer to hunt the nonaggressive bears but they will hunt aggressive bears if they are
the only bears to be hunted.
Part 1: Selection Pressure
1. Obtain ten bears count the number of bears with their arms up (aggressive bears) and the number of bears with their arms down
(nonaggressive bears). Record the number of bears in your data table.
2. As a predator you prefer to hunt the nonaggressive bears, you can hunt the aggressive bears but they take more energy to hunt.
Hunt three nonaggressive bears. If you do not have three nonaggressive bears hunt the difference in aggressive bears and then rest
up after the fight!
3. Each surviving bears reproduce an identical bear. (Yes we are simplifying reproduction for the purpose of this model.)
4. Record the bear population in generation 2.
5. Hunt three nonaggressive bears. If you do not have three nonaggressive bears hunt the difference in aggressive bears.
6. Each surviving bears reproduce an identical bear.
7. Record the bear population in generation 3.
8. Hunt three nonaggressive bears. If you do not have three nonaggressive bears hunt the difference in aggressive bears.
9. Each surviving bears reproduce an identical bear.
10. Record the bear population in generation 4. You should end with a total population of 38 bears.
Part 1: Phenotype Data Table
Generations
Nonaggressive
(arms down)
individuals
Aggressive
(arms up)
individuals
Sum
(Total
Population)
%
Nonaggressive
(arms down)
%
Aggressive
(arms up)
Sum
1
2
3
4
Analysis Questions
1. What happen to the percentage of aggressive bears in the population?
2. In our model we assumed two things that are not true of bear reproduction. First that bears reproduce asexually resulting in one
identical offspring. What is another assumption we made that is not true of bear reproduction?
Part 2: Introduction to Hardy Weinberg
Background: In part 1 of the lab we were only concerned with the phenotype or appearance of the bears. Now we are concerned with
the genotypes or the genetic information of the bears. In the first part of the lab the bears reproduced via asexual reproduction. Asexual
reproduction is when one parent gives all the information to their offspring so that their offspring have exactly the same information.
This information sources is called DNA. So each generation each surviving parent produced an exact copy of itself. In the second part
of the lab we are going to model sexual reproduction. Sexual reproduction is when two parents provide half the genetic information to
their offspring. The resulting offspring is a blend of the two parents' genetic information.
1. After years of genetic research it has been determined that being aggressive is a recessive trait and being nonaggressive is a
dominant trait. Define dominant and recessive.
2. A phenotype is the appearance of the animal and the genotype is the genetic make-up of the individual. The genotype of the
recessive aggressive bear is _______ and the two possible genotypes of the nonaggressive bears are _________ and _________.
3. Define homozygous and heterozygous. Identify which genotypes from question 2 are homozygous and heterozygous.
4. Is it possible to look at the phenotype of the aggressive bears and determine their genotype?
5. The following procedures will allow us to determine the allelic frequency or the frequencies of a and A in the population. These
procedures will also allow us to the number of nonaggressive bears that are heterozygous (Aa) and the number that are homozygous
(AA). Why are we concerned with this?
Procedures
1. The entire class will represent a breeding population of bears. Each person must start with a heterozygous, nonagressive bear.
Collect a nonaggressive bear, two A cards and two a cards.
2. Record the initial genotype of the bear in the Part 2 Data Table.
3. Find a partner.
a. Turn the four cards face down, shuffle them and take the card on top to contribute to produce the first offspring.
b. Your partner will do the same.
c. The two cards will represent the genotype of the first offspring.
d. One person will record the genotype of the first offspring as generation 1 in the Part 2 Data Table.
e. Each partner will collect their card, shuffle them and take the card on the top to produce the second offspring.
f. Your partner will do the same.
g. The two cards will represent the genotype of the second offspring.
h. The other person will record the genotype of the second offspring as generation 1 in the Part 2 Data Table.
4. Now each person will become the generation 1 offspring.
a. Collect a new bear, be sure to collect the correct phenotype.
b. If the generation 1 genotype is different than the parent switch the allele cards to represent the generation 1 genotype.
(Remember you need four allele cards! AA: four A cards, Aa: two A cards and two a cards, aa: four a cards.)
5. Find a new partner and repeat step 3. Record the results as generation 2 in the Part 2 Data Table.
6. Now each person will become the generation 2 offspring. Repeat step 4.
7. Find a new partner and repeat step 3. Record the results as generation 3 in the Part 2 Data Table.
8. Now each person will become the generation 3 offspring. Repeat step 4.
9. Find a new partner and repeat step 3. Record the results as generation 4 in the Part 2 Data Table.
10. Now each person will become the generation 4 offspring. Repeat step 4.
11. Find a new partner and repeat step 3. Record the results as generation 5 in the Part 2 Data Table.
12. Now each person will become the generation 5 offspring. Repeat step 4.
13. Calculate the allele frequency after generation 5.
Part 2: Genotype Data Table
Total Class Population: _________
Total number of alleles in the population (population x 2): _________
Initial Class Frequency:
AA
Aa
aa
My initial genotype:
Generation 1 Genotype:
Generation 2 Genotype:
Generation 3 Genotype:
Generation 4 Genotype:
Generation 5 Genotype:
Generation 5 Class Frequency:
AA
Aa
aa
Number of A alleles present at the fifth generation
Number of offspring with genotype AA
x2
=
A alleles
Number of offspring with genotype Aa
x1
=
A alleles
Total
=
A alleles
p=
TOTAL number of A alleles
TOTAL number of alleles in the population
=
=
Number of a alleles present at the fifth generation
Number of offspring with genotype aa
x2
=
a alleles
Number of offspring with genotype Aa
x1
=
a alleles
Total
=
a alleles
q=
TOTAL number of a alleles
=
=
TOTAL number of alleles in the population
p
q
Analysis Questions
1. Compare the initial values of p and q to the values of p and q after 5 generation.
2. Do the results you obtained in part 2 agree with what you predicted? Why or why not?
3. What major Hardy-Weinberg assumption(s) were not strictly followed in this activity?
Extension
Calculating allelic frequencies and genotypic frequencies is a very important skill in biology. We will use the Hardy Weinberg to
calculate the allelic frequencies and genotypic frequencies. G. H. Hardy was a mathematician and Wilhelm Weinberg was a physician
who independently determined how to calculate the frequencies. Try some calculations! (Show your work!)
Allelic frequency calculation
p+q=1
5
Genotypic frequency calculation
p2 + 2pq +q2 =1
1. Review the definition of the following:
p
q
p2
2pq
q2
2. In Drosophila, fruit flies, the allele for purple eyes is recessive to the wild type (red) eye color. In a population of 1000 individuals 360
have purple eyes.
a. What is the genotype of the purple eyed individuals?
b. What is the frequency of purple eyes in the population?
c. Which of the following represents the frequency of purple eyes?
p
q
p2
d. Calculate the recessive allelic frequency.
e. Calculate the dominant allelic frequency.
f. Calculate the frequency of homozygous dominant individuals in the population.
g. Describe the phenotype of a homozygous dominant individual.
h. Calculate the frequency of heterozygous dominant individuals in the population.
i. Calculate the frequency of dominant phenotypes in the population.
2pq
q2
3. In Drosophila, fruit flies, the allele for vestigial wings (very small nonfunctional wings) is recessive to the wild type (normal) wings. In
a population of 100 individuals 81 have vestigial wings.
a. What is the recessive allelic frequency?
b. How many individuals in the population are homozygous dominant?
c. How many individuals in the population are heterozygous dominant?
4. In the United States about 16% of the population is Rh negative. The allele for Rh negative is recessive to the allele for Rh positive.
The sample population is 2000 people in the United States.
a. What is the recessive allelic frequency?
b. What is the homozygous recessive frequency in the population?
c. How many individuals in the population are homozygous recessive?
d. What is the dominant allelic frequency?
e. What is the homozygous dominant frequency in the population?
f. How many individuals in the population are homozygous dominant?
g. What is the heterozygous frequency in the population?
h. How many individuals in the population are heterozygous?
i. How many individuals in the population are Rh positive?