Lab 8
Mechanisms of
Evolution
OBJECTIVES:
 Gain a better understanding of the principles of Hardy-Weinberg Equilibrium.
 Observe the evolutionary effects of mutation, selection, emigration, and genetic
drift on a breeding population.
PRELAB:
Review the exercise and bring a calculator to lab.
MATERIALS:
2 colored index cards per student
Box with numbered slips of paper equal to half the students in the class
(e.g. if there are 30 students, the papers will be numbered 1, 2, 3…15)
BACKGROUND:
Gregor Mendel, and Austrian monk, published his work with the heredity of garden peas
in 1865. He set forth his now-famous Laws of Heredity. These Laws permit one to
predict the genotypes and phenotypes of offspring from a particular pair or pairs of
breeding parents. Unfortunately, they do not enable us to know anything about the
frequencies of different alleles in a population made up of many types of breeding parents
or the subsequent population made up of their offspring.
In 1908, working independently of one another, G.H. Hardy (an English mathematician)
and Wilhem Weinberg (a German physician) developed a technique for determining
allelic frequencies in populations. Under certain conditions, amazingly, an equilibrium of
allelic frequencies develops which has become known as the Hardy-Weinberg principle.
The Hardy-Weinberg principle states that the frequency of any allele will remain constant
generation after generation, provided that there is: a) random breeding; b) no mutation;
c) no immigration or emigration; d) no selection against any phenotype; and e) no genetic
drift.
We are going to do an exercise that demonstrates the Hardy Weinberg principle. We
shall see what occurs when all of the conditions in the Hardy-Weinberg principle are
maintained. Then we shall violate various conditions and see what happens to allelic
frequencies.
PROCEDURES:
1.
Divide the class into two equal groups.
2.
Each person in Group 1 (the “females”) chooses a number from the box.
These individuals will keep that designated number for the duration of the
experiment. Return the paper to the box.
3.
Instructor distributes two colored cards to each student.
4.
Count the total number of each color card. Count the number of students that
are homozygous for Color 1, heterozygous, and homozygous for Color 2.
Complete the appropriate sections in Table 1.
5.
Determine the allele and genotype frequencies in the population. Complete
the appropriate sections of Table 1.
6.
Each student should place one card in each hand.
7.
Each person in Group 2 (the “males”) chooses a number from the box.
8.
The two students with the same number “mate” by exchanging the card in the
hand designated by the instructor.
9.
Repeat steps 4 – 8 for 3 more generations.
10.
The instructor replaces two of the Color 1 alleles with two of the Color 2
alleles, introduction mutation. Repeat steps 4 – 8 for 3 generations, each time
with two more “mutations.”
11.
The instructor redistributes colored cards so that the allele frequencies are 0.5.
Selection is introduced by removing any student who is homozygous for
Color 2 from the breeding population. (If a “female” “dies” then her number
is removed from the box.) Repeat steps 4 – 8 for 3 generations, each time
removing homozygous Color 2 individuals from the population. (If someone
cannot find a mate one generation, he or she stays in the breeding population
and participates in the next round of mating.)
12.
Everyone returns to the breeding population and all numbers are returned to
the box. Now emigration is introduced. The instructor will choose two
students to leave the breeding population. Repeat steps 4 – 8 for 3
generations, each time removing 2 students from the population. (If a
“female” “emigrates” then her number is removed from the box.)
13.
Everyone returns to the breeding population and all numbers are returned to
the box. Now genetic drift is introduced. A catastrophic event eliminates half
of the breeding population regardless of genotype. Repeat steps 4 – 8 for each
generation.
TO HAND IN
Lab 8
Name:
COLOR 1 =
COLOR 2 =
TABLE 1.
(F = frequency)
Gen. #
1
2
3
4
5
6
7
8
9
10
11
12
13
Alleles
Pop. Color
Total 1
#
F
Color
2
# F
Genotypes
Your
Pop. Homozy. Heterozy. Homozy. Genotype
Total Color 1
Color 2
#
F
#
F
#
F
Lab 8
Name:
1. If Color 1 is dominant, then what are the phenotype frequencies?
Generation #
1
2
3
4
5
6
7
8
9
10
11
12
13
Dominant
Recessive
2. The Hardy-Weinberg equations state that p + q = 1 and p2 + 2pq + q2 = 1. If p =
the frequency of Color 1 alleles and q is = the frequency of color 2 alleles,
determine if generations 1, 4, 7, 10 and 13 are approximately in Hardy-Weinberg
equilibrium.
3. In general, what happened to the allele frequencies when:
a. None of the rules were violated?
b. Mutation was introduced?
c. Selection was introduced?
d. Emigration was introduced?
e. Genetic drift was introduced?