Name _____________________________________Per____
Anole Lizard Trait Distribution Lab
Today we will look at how traits are distributed in nature. We will use human arm length and anole lizard arm
length to study genetic diversity and trait distribution.
1. What is your arm length? Measure from your armpit to the tips of your fingers. _____________
2. Create a graph of your class arm lengths below:
3. What do you think the graph would look like if there was a sudden
change in environment and only long armed individuals ended up surviving?
(just draw the general shape of the graph)
4. What do you think the graph would look like if there was a sudden
change in environment and all the individuals with medium length arms died
out? (just draw the general shape of the graph)
Other organisms also show variation in limb length. Studies on brown anolis
lizards demonstrate that lizard populations change limb length when exposed
to predators.
Researchers led by Jonathan Losos of Harvard University studied brown
anole lizards on 12 small islands in the Bahamas. They introduced a larger,
predatory lizard (​Leiocephalus carinatus​) to six of the islands, while keeping
six other control islands predator-free.
The scientists counted, marked and measured lizards at the beginning of the
study, after six months, and again after 12 months. After six months, the anole
populations dropped by half or more on islands with predators.
The data for the experiment is shown in Data Set #1. Plot the data for the initial population and the population after six
months in the graph below:
1. How is the graph of the initial leg lengths different from the graph of the leg lengths after six months?
List TWO differences.
2. How do you think the leg length help lizards survive in the environment with the predator?
3. Which graph looks most similar to the
graph you just created of limb length?
(Circle one)
4. After 12 months, the researchers returned to the islands and measured the lizards’ limb lengths again.
The results are summarized in data set #2. What happened to lizard limb length after 12 months?
5. WHY did lizard limb length change after 12 months? Use Data Set #3 to help you answer this question:
6. A scientist took DNA samples from two lizard populations on the islands. His data is presented in Data
Set #4. The genes for each lizard in the population is listed next to the lizard. For each population,
count up the total number of each allele in the population:
St. Lucia Population
Barbados Population
A alleles
a alleles
C alleles
c alleles
G alleles
g alleles
7. Which population is more genetically diverse (has more variety in genes)?
8. Assume that the “G” allele codes for resistance to a fungal disease. Lizards that have the “G” allele do
not get the disease and therefore survive. Lizards that do not have the “G” gene and only have the “g”
allele get the disease and die.
a. Which population has a higher frequency of the G allele? _____________
b. Which population is more likely to survive the fungal infection? ___________
9. Assume that the “C” allele codes for having a large body and the “c” allele codes for having a small
body. A ship brings a new invasive rodent to the islands and lizards with large bodies are able to
survive because they can defend themselves against the large rodent. Individuals with the “c” allele
cannot defend themselves so they end up dying.
a. Which population has a higher frequency of the “C” allele? ______________________
b. Which population will be more likely to survive with the new predator? _________________
10. Why is genetic diversity (having lots of different genes) important in a population?
11. Zoos look at genetic diversity to help their populations survive when in captivity (in the zoo). If a
population in a zoo has low genetic diversity, the zookeepers will often bring in an animal from another
zoo to mate and introduce new genes into the population. The Milwaukee Zoo currently has a
population of brown anole lizards in its reptile exhibit that are exhibiting low genetic diversity.
Lizard at
Milwaukee Zoo
Lizard at St. Louis
Zoo
Lizard at San Diego
Zoo
Lizard at
Chicago Zoo
FF
FF
ff
Ff
bb
Bb
BB
bb
pp
pp
Pp
pp
kk
kk
kk
kk
Qq
qq
qq
QQ
a. If you are a zookeeper at the Milwaukee zoo and you have the population of lizards listed
above, which individual would you select to come breed with your lizard in order to increase
genetic diversity?
b. Why did you choose this individual?
12. Think back to the lizard population in Data Set #4 that lives on Barbados. Given what you just found
out in question #11, how could you increase the genetic diversity of the lizard population in Barbados?
DATA SET #1:
Initial Leg
Length
Number of
lizards with
each leg length
Leg Length 6
Months After
Predator
Introduced
Number of
lizards with
each leg length
16 mm
1
16 mm
0
20 mm
6
20 mm
0
24 mm
11
24 mm
0
28 mm
15
28 mm
1
32 mm
17
32 mm
3
36 mm
12
36 mm
5
40 mm
8
40 mm
8
44 mm
3
44 mm
7
48 mm
1
48 mm
3
_______________________________________________________________________________________
DATA SET #2
DATA SET #3
Initial Leg
Length
Number of
lizards with
each leg
length
16 mm
2
20 mm
5
24 mm
12
28 mm
16
32 mm
16
36 mm
12
40 mm
7
44 mm
2
48 mm
1
*Perch height refers to how high up the lizards are perched in the trees.
Perch diameter refers to the diameter (width) of the branch that the
lizards are perched on.
DATA SET #4