Download Leaping Lizards: Gene Frequency Activity

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Exploring Natural Selection and Allele Frequencies: Leaping Lizards!
Name: ______________________________________________________ Hour: _____________________
Part 1: Do-Now Activity (Read, Think, Record)
Begin by reading the first two sections (introduction and “Founder effect versus natural selection”) of the
article, Lizards Released and Stranded on Islands Show Evolution at Work. As you read, highlight words
and/or phrases that represent key terms we have discussed over the course thus far. Underline new terms that
are familiar and that you believe are critical to understanding the article. Circle any terms that are unfamiliar to
you (science-related or not).
As you read, address the following questions:
1. How are natural selection and founder effect different?
2. If lizards from a forested island had been introduced to a scrubland island, what do you predict will
happen to leg length? Please write in the form of a hypothesis (If… then…).
3. What question would you ask the researchers of this study? What do we need to know/understand from
the study to interpret the data? What is unclear? Come up with at least one testable question.
Lizards Released and Stranded on Islands Show Evolution at Work
Joseph Castro, LiveScience Staff Writer
Like something out of a reality-TV show, scientists released pairs
of small lizards onto tiny uninhabited islands in the Bahamas and
watched what happened. Rather than playing for money or fame,
the reptiles played for survival, allowing the voyeuristic
researchers to witness the interaction between evolutionary
processes rarely observed in nature.
After several years and multiple generations of lizards, the
researchers found that both natural selection — whereby traits
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that enhance survival get passed down from generation to generation — and random processes contributed to
the animals' genetics and their physical characteristics.
"We were actually able to see these processes and document them happening in a natural environment," Jason
Kolbe, a biologist at the University of Rhode Island who led the study, told LiveScience. "We know that islands
are colonized by new species over time, but we are rarely there to see it happen."
When a few individuals of a species colonize a new area, their offspring undergo what is known as the founder
effect, which is a change in genetics or physical characteristics. Because of the small number of founding
individuals, the new population experiences a loss in genetic variability, often resulting in individuals that are
physically and genetically different from their source population.
In addition to random processes like the founder effect, which has everything to do with the random genes that
get passed down from the first individuals on the island, populations also experience natural selection, where
they adapt to their environment and pass on beneficial traits to their offspring.
Founder effect versus natural selection
To find out, Kolbe and his colleagues randomly selected male-female pairs of brown anole
(Anolissagrei) lizards from Iron Cay, an island in the Bahamas, and released them on seven smaller islands in
2005. The smaller islands, whose lizard populations had been wiped out by a recent hurricane, are very similar
to one another, populated by the same types of insects, birds and vegetation (short scrubs), but very different
from Iron Cay, which is forested.
Previous research has shown that forest anoles have longer hind limbs than their scrub cousins — long limbs
allow lizards to move quicker across thick branches, while short limbs give lizards the stability they need to
walk along narrow perches.
The researchers predicted that over time, the lizards in their experiment would develop shorter hind
limbs than those of the lizards on Iron Cay, but they didn't know what role the founder effect would play in
the matter.
After the first year of the study, the researchers immediately noticed a founder effect — the offspring of the
original lizards plopped onto the islands in 2005 had less genetic variability than the Iron Cay lizards.
"There were also significant differences in hind-limb length among the islands, even though the lizards were all
from same source population," Kolbe said. Since the founder effect is a random process independent of the
environment, there was no pattern to the length of the lizards' hind limbs and apparently no relationship
between limb length and perch diameter, he explained.
Over the next few years, however, a pattern did emerge for the lizards on the experimental islands. With each
generation, their hind limbs got shorter, making them better suited for their environment. But the founder effect
wasn't completely snuffed out: Lizard populations with the longest limbs in 2006 still had the longest limbs
three years later.
“Both processes seem to be important here,” Kolbe said. "Original differences were created that were random,
and then the environment decreased their mean hind-limb length."
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Part 2: Class Discussion
Question Board  What do we want to know? How can we further explore the concepts of natural selection,
genetic diversity, and allele frequencies? What implications does this change in phenotype have for the lizard
populations?
Please record your notes from the discussion, including any questions posed by other groups that you found
interesting:
Part 3: Pre-lab – Compiling Background Information
In this activity, we will take a closer look at how natural selection is playing out in these small populations of
Anolis lizards in the Bahamas. Evolution, on a genetic level, is a change in the frequency of alleles in a
population of a period of time.
For the phenotype of the lizards to have changed over time (longer legs to shorter legs), what must be
true about the frequency of the allele for shorter legs?
Why are shorter legs selected for on the new island?
With your partner, you will collect data that illustrates the impact that genetics can have on the evolution of a
population of organisms. For our investigation, we will be using beans to represent the lizards in our breeding
population.
Alleles and Assumptions:
 The allele for long legs is F (white beans)
 The allele for short legs is f (red beans)
 The genotype FF (homozygous) results in long legs
 The genotype ff (homozygous) results in short legs
 The genotype Ff (heterozygous) results in short legs
 The allele frequencies are equal at the start of our simulation.
 Individuals with the genotype FF are not best suited to the new environment. We will therefore assume
that these individuals do not survive to reproduce and are removed from the population.
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WHY are these individuals NOT best suited for the new environment?
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What is your hypothesis for how (or if) the allele frequencies will change over the 10 generations?
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Part 4: Lab Exercise
1. You have been given two “allele pool” dishes, each with 50 beans:
a. White beans represent the F allele, which is for long-legged lizards
b. Red beans represent the f allele, which is for short-legged lizards
2. Place all 100 beans into your “gene pool” and shake it up!
3. Without looking at the beans (close your eyes or look away), select two beans at a time, place them on
a corresponding “lizard” on the Lizard Genotype Log and record the results (tally mark) on the Gene
Frequency Data form next to “Generation 1.”
a. What does each bean represent? Each pair of beans?
b. Why do you select 2 beans?
c. How many individuals (lizards) will you have after this initial allele sorting (“mating”)?
4. Record the number of F and f alleles as well as the total alleles. Calculate the initial gene frequencies.
We will work through Generation 1 together! Be sure to write out the steps so that you can use this
example to complete the rest of the chart for all 10 generations.
5. Death!! Some of our lizards are not going to survive to reproduce offspring for the next generation.
a. Which ones will die? (Genotype and bean color) ____________________________
**Remove these from the population before calculating frequencies for the current generation.**
6. Using only the surviving lizards, place the alleles (beans) back in the “gene pool,” mix it up, and
simulate mating that will result in Generation 2. Repeat steps #4-7 until you have completed 10
generations.