Download Estimating Allele Frequencies for a Specific Trait within a Sample

Simulating Hardy-Weinberg Effects on Evolution
Integrated Science 4
5/13
Name:
Per:
Background
Understanding natural selection can be confusing and difficult. People often think that organisms
consciously adapt to their environments. For example, that the peppered moth can change its color, the
giraffe can permanently stretch its neck, the polar bear can turn itself white – all so that they can better
survive in their environments. In reality, populations of organisms, not the individuals, adapt and
evolve over time under the influence of natural selection and genetic drift. In this lab, you will use fish
crackers to help further your understanding of measuring evolutionary change using allele frequencies
and genotype frequencies, which together reflect the genetic make-up of a population.
In addition, you will simulate the Hardy-Weinberg conditions and practice using the HardyWeinberg mathematical equations to determine if evolution has occurred over time.
Hardy-Weinberg Conditions: 1. large population, 2. random mating, 3. no mutation, 4. no migration,
5. no selection
Hardy-Weinberg Mathematical Equations: p + q = 1 and p2 + 2pq + q2 = 1
Basically, the Hardy-Weinberg equation describes the status quo. If the five conditions are met, then
no change will occur in either allele or genotype frequencies in the population. The value of this type of
model is that it provides a yardstick by which changes in allele frequency, and therefore evolution, can
be measured. One can look at a population and ask: Is evolution occurring with respect to a particular
gene allele?
Facts About The Fish
 In this simulation, goldfish crackers are the natural prey of the terrible fish-eating shark – YOU!
 Fish come with two phenotypes: gold and white
- The allele for gold color is recessive, so fish that have this phenotype are homozygous
recessive for this gene (ff).
- The allele for white color is dominant, so fish that have this phenotype are either homozygous
dominant (FF) or heterozygous (Ff) for this gene.
 New fish are born every year and the birth rate equals the death rate.
 Births are simulated by reaching into the “ocean” of spare fish and randomly choosing the
replacement fish.
Hypothesis
Read through the simulations first. Based on the simulations and the reading above, predict how
allele frequencies (p and q) will be affected by each of the following:
If no selection occurs, then…
If selection occurs due to a
homozygous recessive disadvantage
(selected against), then…
If genetic drift occurs due to a small
population, then…
Simulation 1: The Effects of No Selection
 Part A. Team Data for No Selection
1. Randomly choose a study population of 20 fish from the ocean. Note: there are equal numbers of
gold and white fish in the ocean.
2. Count gold and white fish in the initial population of 20 and record your individual data for
Generation 1 in Data Table 1.
3. From your initial population of 20 fish, randomly choose 6 and eat them.
4. Recall that the birth rate equals the death rate, so “give birth” to 6 new fish, by randomly choosing 6
from the “ocean”.
5. Count gold and white fish in the population for the second generation and record your data for
Generation 2 in Table 1.
6. Repeat procedures 3 through 5 for Generations 3, 4, 5 and 6 (final). Remember, for each generation,
eat randomly, replace randomly and record all data in Table 1.
Data Table 1: No Selection - Team Data
# of White
Fish
Generation
# of Gold
Fish
1 (initial)
2
3
4
5
6 (final)
 Part B. Class Data for No Selection
1. Determine the total number of white colored fish and the total number of gold colored fish in
Generation 1 for your entire class. Record these values in Table 2.
2. Determine the total number of white colored fish and the total number of gold colored fish in
Generation 6 for your entire class. Record these values in Table 2.
3. Using the Hardy-Weinberg Mathematical equations, calculate allele frequencies (p and q) and
genotype frequencies (p2, 2pq and q2) of fish color for Generation 1 and Generation 6 for the entire
class population. Show your work below and record the gene frequencies for the initial and final
Instructions for Calculating Frequencies:
To determine the frequency of the gold genotype (q2, homozygous recessive individuals), divide the number of gold
individuals in the population by the total number of fish in the population. Once q2 is determined, calculate q
(recessive alleles), then p (dominant alleles), and then 2pq (heterozygous individuals) and p2 (homozygous recessive
individuals).
populations in Table 2. Round all decimal values to the hundredths place.
Data Table 2: No Selection - Class Data
Generation
1 (initial)
6 (final)
# of White
Fish
# of Gold
Fish
p
q
p2
2pq
q2
No Selection - Class Data Initial Generation Calculations
No Selection - Class Data Final Generation Calculations
Simulation 2: The Effects of Selection
 Part A. Team Data for Selection
1. Randomly choose a study population of 20 fish from the ocean. Note: there are equal numbers of
gold and white fish in the ocean.
2. Count gold and white fish in the initial population of 20 and record your individual data for
Generation 1 in Table 3.
3. To simulate selection, the predator will no longer eat randomly. You, the terrible fish-eating sharks,
much prefer to eat the gold colored fish. You will eat ONLY gold colored fish unless none are
available, forcing you to eat white fish in order to survive. So… eat 6 gold colored fish if they are
available in your initial generation. If not, supplement with white.
4. Recall that the birth rate equals the death rate, so “give birth” to 6 new fish, by randomly choosing 6
from the “ocean”.
5. Count gold and white fish in the restored population and record your data for Generation 2 in Table
3.
6. Repeat procedures 3 through 5 for Generations 3, 4, 5 and 6 (final). Remember, for each generation,
eat selectively, replace randomly and record all data in Table 3.
Data Table 3: Selection - Individual Data
Generation
# of White
Fish
# of Gold
Fish
1 (initial)
2
3
4
5
6 (final)
 Part B. Class Data for Selection
1. Determine the total number of white colored fish and the total number of gold colored fish in
Generation 1 for your entire class for the selection simulation. Record these values in Table 4.
2. Determine the total number of white colored fish and the total number of gold colored fish in the
Generation 6 for your entire class for the selection simulation. Record these values in Table 4.
3. Using the Hardy-Weinberg Mathematical equations, calculate allele frequencies (p and q) and
genotype frequencies (p2, 2pq and q2) of fish color for the Generation 1 and Generation 6 for the entire
class population. Show your work below and record the gene frequencies for the initial and final
populations in Table 4. Round all decimal values to the hundredths place.
Data Table 4: Selection - Class Data
Generation
# of White
Fish
# of Gold
Fish
p
q
p2
2pq
q2
1 (initial)
6 (final)
Selection – Class Data Initial Generation Calculations
Selection – Class Data Final Generation Calculations
Simulation 3: The Effects of Genetic Drift
 Part A. Team Data for Genetic Drift
1. Randomly choose a study population of 6 fish from the ocean. Note: there are equal numbers of gold
and white fish in the ocean.
2. Count gold and white fish in the initial population of 6 and record your individual data for
Generation 1 in Table 5.
3. From your initial population of 6 fish, randomly choose 2 and eat them.
4. Recall that the birth rate equals the death rate, so “give birth” to 2 new fish, by randomly choosing 2
from the “ocean”.
5. Count gold and white fish in the population for the second generation and record your data for
Generation 2 in Table 5.
6. Repeat procedures 3 through 5 for Generations 3, 4, 5 and 6 (final). Remember, for each generation,
eat randomly, replace randomly and record all data in Table 5.
Data Table 5: Genetic Drift - Individual Data
Generation
# of White
Fish
# of Gold
Fish
1 (initial)
2
3
4
5
6 (final)
 Part B. Class Data for Genetic Drift
1. Determine the total number of white colored fish and the total number of gold colored fish in
Generation 1 for your entire class for the selection simulation. Record these values in Table 6.
2. Determine the total number of white colored fish and the total number of gold colored fish in the
Generation 6 for your entire class for the selection simulation. Record these values in Table 6.
4. Using the Hardy-Weinberg Mathematical equations, calculate allele frequencies (p and q) and
genotype frequencies (p2, 2pq and q2) of fish color for the Generation 1 and Generation 6 for the entire
class population. Show your work below and record the gene frequencies for the initial and final
populations in Table 6. Round all decimal values to the hundredths place.
Data Table 6: Genetic Drift - Class Data
Generation
# of White
Fish
# of Gold
Fish
p
q
p2
2pq
q2
1 (initial)
6 (final)
Genetic Drift – Class Data Initial Generation Calculations
Genetic Drift – Class Data Final Generation Calculations
Graphs
1. Prepare a graph of the class results that represents the effects of no selection on the allele frequencies
(p and q) of the initial and final populations.
2. Prepare a graph of the class results that represents the effects of selection on the allele frequencies (p
and q) of the initial and final populations.
3. Prepare a graph of the class results that represents the effects of genetic drift on the allele frequencies
(p and q) of the initial and final populations.
Discussion
1. Reflect on each hypothesis, and state whether each was supported or refuted. Explain why using
data values to support your conclusion.
a. No Selection:
b. Selection:
c. Genetic Drift:
2. What five conditions must exist for gene frequencies to stay the same over time?
3. What process occurs when there is a change in gene frequencies over long periods of time?
4. Explain what would happen if conditions changed and the recessive trait offered a selective
advantage (was selected for rather than against)?
5. What would happen if it were more advantageous to be heterozygous? Would there still be
homozygous fish in the population over time? Explain.
Conclusion
6. Design an experiment to show how one of the following effects allele frequencies: a) migration,
b) isolation, c) mutations. Attach additional paper as needed.