Download Mechanisms of Evolution Lab

Mechanisms of Evolution
CLASS SET
Purpose: Describe how allele frequencies change for each mechanism of evolution.
Investigative Question: How do the mechanisms of evolution change allele frequencies?
Introduction:
Selective pressures act on phenotypes of individuals, which can change the allele frequency of a population. Other mechanisms can
also change allele frequencies in populations, in this lab the mechanisms of gene flow, genetic drift, the bottleneck effect, founder
effect, and sexual selection will be studied.
Procedure:
1.
2.
3.
4.
Read the lab introduction.
Complete the pre-lab.
Get the pre-lab checked off.
Gene Flow
a.
Start with 2 populations, one in each cup.
b.
Each population should have 20 individuals, 5 of each phenotype.
c.
Record starting populations in data table.
d.
Each partner should pick up one cup.
e.
Place hand over the top of the cup, leaving a slight opening next to an edge.
f.
Tilt the cup and gently shake it until 7 individuals are removed from the population.
g.
Take the 7 individuals and place them into the other cup.
h.
Record the number of each phenotype in the data table.
i.
Repeat steps d-h twice more to complete 2 more generations.
j.
Get checked off.
5. Genetic Drift; Bottleneck Effect
a.
Start with a population of 80 individuals, 20 of each phenotype. Yes. Count them all.
b.
Record the number of each phenotype in the data table.
c.
Put all individuals into one cup.
d.
Place hand over cup and gently shake to mix the phenotypes together.
e.
Place hand over the top of the cup, leaving a slight opening next to an edge.
f.
Tilt the cup and gently shake it until 10 individuals are removed from the cup.
g.
The 10 individuals on the lab bench survived a natural disaster.
h.
Record the number of each phenotype in the data table.
i.
Multiply this number by two for each generation.
6. Genetic Drift; Founder Effect
a.
Start with a population of 80 individuals, 20 of each phenotype. Yes. Count them all.
b.
Record the number of each phenotype in the data table.
c.
Put all individuals into one cup.
d.
Place hand over cup and gently shake to mix the phenotypes together.
e.
Place hand over the top of the cup, leaving a slight opening next to an edge.
f.
Tilt the cup and gently shake it until 10 individuals are removed from the cup.
g.
The 10 individuals have traveled to a new land and are founders of a new population.
h.
Record the number of each phenotype in the data table.
i.
Multiply this number by two for each generation.
7. Sexual Selection
a.
Complete the sexual selection questions using the following graphs:
i. Widowbirds of Kenya
ii. Guppies
Names: _______________________
Mechanisms of Evolution – Answer Sheet
Period: _______________________
Pre-Lab: Make sure that you have read the lab introduction.
1.
What does natural selection act on?
2. What does change in a population really refer to?
3. What are the “other” mechanisms of evolution?
Gene Flow:
1.
What is gene flow?
2.
How many populations are required for gene flow to work?
3.
Follow the instructions for gene flow.
Population 1:
Generation 1
Phenotype
# of
Individuals
Allele
Frequency
Generation 2
# of
Individuals
Allele
Frequency
Generation 3
# of
Individuals
Allele
Frequency
Generation 4
# of
Individuals
Allele
Frequency
Population 2:
Generation 1
Phenotype
# of
Individuals
Allele
Frequency
Generation 2
# of
Individuals
Allele
Frequency
Generation 3
# of
Individuals
Allele
Frequency
Generation 4
# of
Individuals
Allele
Frequency
4.
How do the fourth generations compare to the first generations for each population? Be specific.
5.
How do the new populations compare to each other?
6.
What is a real-life example of gene flow?
Genetic Drift:
1.
What is genetic drift?
2.
What must be true about a population in order for genetic drift to work?
Bottleneck Effect:
1.
What is the bottleneck effect?
2.
Does it occur before or after genetic drift?
3.
Follow the instructions for genetic drift; bottleneck effect.
Generation 1
Phenotype
Total
Individuals
# of
Individuals
80
Allele
Frequency
Generation 2
# of
Individuals
Allele
Frequency
Generation 3
# of
Individuals
10
20
Allele
Frequency
Generation 4
# of
Individuals
Allele
Frequency
40
4.
On a separate sheet of paper graph the allele frequencies of generations 1 and 2 to show the shifting selection. Use
a dotted line for generation 1 and a solid line for generation 2.
5.
What kind of selection does this graph most closely match?
6.
How does the final population compare to the original population? Be specific.
7.
Why is it more accurate to compare allele frequencies rather than the number of individuals for each phenotype?
Founder Effect:
1.
What is the founder effect?
2.
Does it occur before or after genetic drift?
3.
Follow the instructions for genetic drift; founder effect.
Generation 1
Phenotype
# of
Individuals
Total
Individuals
Allele
Frequency
80
Generation 2 “Founders”
# of
Individuals
Allele
Frequency
Generation 3
# of
Individuals
10
Allele
Frequency
20
Generation 4
# of
Individuals
Allele
Frequency
40
4.
On a separate sheet of paper graph the allele frequencies of generations 1 and 2 to show the shifting selection. Use
a dotted line for generation 1 and a solid line for generation 2.
5.
What kind of selection does this graph most closely match?
6.
How does the fourth generation compare to the first generation? Be specific.
7.
Compare and contrast the population changes between bottleneck effect and founder effect.
Sexual Selection:
1.
What is sexual selection?
2.
What are two kinds of sexual selection? Give an example of each.
3.
Widowbirds of Kenya
The data in the graph was collected during an experiment involving widowbirds in Kenya. The biologist was studying the
relationship between tail feather length and reproductive success in males of this species. The average number of nesting
sites was used to measure reproductive success (biological fitness) and was recorded for four groups of birds. Tail feathers
were artificially shortened in one group. Two groups were used as control groups, and tail feathers were artificially
lengthened in the fourth group.
4.
a.
What is the average nest per male bird in the artificially shortened tails group?
b.
What are the average nests per male of each control group?
c.
How many nests did the group with artificially lengthened tails average?
d.
Which population shows the greatest reproductive success and therefore are the most biologically fit?
e.
What kind of sexual selection is this?
f.
How will this species change overtime due to sexual selection?
g.
What opposing selective pressure might limit tail length in male widowbirds? Explain how this pressure will oppose the
selective pressure of mate choice.
Guppies
The graph shows sexual selection patterns in guppies (fish) using data collected during three experiments that investigated
female guppies preference for males with specific tail sizes. In each experiment, female guppies were given the choice of 2
males to mate with, each having a different tail size: large vs. small, large vs. medium, and medium vs. small.
5.
a.
What tail sizes were compared during each experiment?
b.
Why might the difference in preference be larger in experiment 1 than in experiment 2?
c.
What is the relationship between tail size in male guppies and female preference for mates?
d.
What kind of sexual selection is this?
e.
Are there any opposing selective pressures that could limit the tail size of male guppies? Explain how this pressure
will oppose the selective pressure of mate choice.
Look up an example of the other kind of sexual selection. Give the species name, explain which sex competes, and how
they compete. Also, explain how this has changed the species over time.