Download Natural Selection Lab

Name______________________
Period_______
Lab Activity: The Effect of Natural Selection on Populations
Materials
 10 red beads
 10 blue beads
 1 plastic bag or other container per person
 1 container for dead offspring per table
Pre-lab questions
1. What is natural selection?
2. What is the result of natural selection over many generations?
Procedure
1. Work as an individual. Each person’s gene pool represents a segment of the
total population.
2. Whenever the music stops, you mate using the rules of the particular part (A-D)
producing two offspring (one for each of your populations).
Part A – Random Mating
3. Place 10 Blue beads and 10 Red beads into your “population” container.
Assume that Blue beads represent the dominant allele (Widow’s Peak – T) and
Red represents the recessive allele (No Widow’s Peak – t). Mix them up before
each mating.
4. When the music begins, walk randomly around the room. When the music stops,
mate with the person nearest you. During mating, each person contributes one
allele to each offspring. After mating, place the offspring you are keeping back
into the population container.
5. This will repeat 7 more times, so you have produced 8 offspring.
6. Count and record the number of each allele for the whole population in Table 1.
Also calculate allele frequencies using the total number of alleles.
7. To calculate the frequencies of alleles in the population, divide the number of a
particular allele by the total number of genes.
8. Create a graph representing the initial and final population allelic
frequencies for this round.
Part B – Differential Survival – Fatal Autosomal Recessive Disorder (Tay Sachs)
1. Place 10 Blue beads and 10 Red beads into your “population” container.
Assume that Blue beads represent the dominant allele (normal gene – T) and
Red represents the recessive allele (Tay Sachs mutation – t). Mix them up
before each mating.
2. When the music begins, walk randomly around the room. When the music stops,
mate with the person nearest you. During mating, each person contributes one
allele to each offspring. Offspring with a homozygous recessive genotype (2
recessive alleles) automatically die and those alleles are removed from
your populations by placing them into one of the “Dead” containers at each
table. After mating, place the offspring you are keeping back into the population
container.
3. This will repeat 7 more times, so you have produced 8 offspring.
4. Count and record the number of each allele for the whole population in Table 2.
Also calculate allele frequencies using the total number of alleles.
5. To calculate the frequencies of alleles in the population, divide the number of a
particular allele by the total number of genes.
6. Create a graph representing the initial and final population allelic
frequencies for this round.
Part C – Sexual Selection – Mate Selection Based on Height
1. The class will be divided in half and assigned a gender. If you are 5’7” or
taller, place 15 Blue beads and 5 Red beads into your “population” container. If
you are shorter than 5’7”, place 5 Blue beads and 15 Red beads into your
“population” container. Assume that Blue beads represent the dominant allele
(T) and Red represents the recessive allele (t). Mix them up before each mating.
2. When the music begins, walk randomly around the room. When the music stops,
mate with the person nearest you who is taller than you. During mating, each
person contributes one allele to each offspring. After mating, place the offspring
you are keeping back into the population container.
3. Keep count of how many rounds you do not mate. You will randomly
remove this number of offspring (2 alleles each) from your gene pool at the
end.
4. This will repeat 7 more times, so you have produced 8 offspring.
5. Count and record the number of each allele for the whole population in Table 3.
Also calculate allele frequencies using the total number of alleles.
6. To calculate the frequencies of alleles in the population, divide the number of a
particular allele by the total number of genes.
7. Create a graph representing the initial and final population allelic
frequencies for this round.
Part D – Heterozygous Advantage – Simulating the Sickle Cell Condition
1. Place 10 Blue beads and 10 Red beads into your “population” container.
Assume that Blue beads represent the dominant allele (normal hemoglobin –
T) and Red represents the recessive allele (sickle cell hemoglobin – t). Mix
them up before each mating.
2. When the music begins, walk randomly around the room. When the music stops,
mate with the person nearest you. During mating, each person contributes one
allele to each offspring. Offspring with a homozygous dominant genotype (2
dominant alleles) (flip a coin, heads dead from malaria). Offspring with
homozygous recessive (2 recessive alleles) always die from sickle cell
anemia. Offspring with the heterozygous genotype (1 dominant/1
recessive) always live. Those alleles of the dead are removed from your
populations by placing them into one of the “Dead” containers at each
table. After mating, place the offspring you are keeping back into your
population container.
3. This will repeat 7more times, so you have produced 8 offspring.
4. Count and record the number of each allele for the whole population in Table 4.
Also calculate allele frequencies using the total number of alleles.
5. To calculate the frequencies of alleles in the population, divide the number of a
particular allele by the total number of genes.
6. Create a graph representing the initial and final population allelic
frequencies for this round.
Table 1 Random Mating
Total
Generation # of T
alleles
alleles
1
%T
# of t
alleles
Total
alleles
50%
%t
50%
8
Table 2 Differential Survival – Fatal Autosomal Recessive Disorder (Tay Sachs)
Total
%T
# of t
Total
%t
Generation # of T
alleles
alleles
alleles
alleles
1
50%
50%
8
Table 3 Sexual Selection – Mate Selection Based on Height
Total
%T
# of t
Total
Generation # of T
alleles
alleles
alleles
alleles
1
%t
8
Table 4 Heterozygous Advantage – Simulating the Sickle Cell Condition
Total
%T
# of t
Total
%t
Generation # of T
alleles
alleles
alleles
alleles
1
50%
50%
8
Results
Analysis
Compare the beginning and ending frequencies of each trial and explain what you
observe in terms of selection, differential survival, and biological fitness.