Questions:
1.
In the gizmo, there are 10 insects on a leafy green backdrop.
a. Mouse over one of the bugs. The color of each bug is controlled by genes on the two
chromosomes shown. There are three genes on each chromosome that control the
color of the bug, for a total of six.
b. The genotype of a bug is the combination of alleles it contains. What are the alleles in
the genotype of the selected bugs? Do all of the ugs in the first generation have the
same genotype?
c. The phenotype of a bug is what it actually looks like. In the Gizmo, this is expressed in
RGB (red, green, blue) values. What color does RGB values of 255, 255, 255 correspond
to?
d. Notice that the fitness of each bug is also listed. The greater the fitness of a bug, the
greater its chance of survival. When a bug is exactly the same color as the background,
its fitness is 100%. What background color would lead to 0% fitness for the bugs
shown?
2. Use the red, green, and blue sliders to set the background to any color you like. Check that the
Sim. Speed slider is set to its slowest setting, and click Play. Observe for a few generations.
a. The bugs in the simulation reproduce sexually. They select a mating partner randomly,
and each parent contributes a single chromosome to each offspring bug. The offspring
are displayed to the right of the parent pair. How many offspring does each pair of bugs
produce?
b. Predation is represented by birds. How many bugs are eaten by birds in each
generation? How many bugs survive?
c. The average fitness is displayed below the simulation. What is the average fitness now?
From the start of the simulation, has the average fitness changed?
3. Click Pause when you see a circled bug among the offspring. The circles indicate the presence of
random mutations that affect the color of the bugs. In this Gizmo, mutation rates are much
higher than in nature.
a. What is the color of the mutant bug?
b. Mouse over the mutant bug to examine its genome. Which gene mutated? What was
the color of the new allele? (Hint: Compare this bug’s genome with the genomes of its
parents, which are the pair of bugs to the left.)
c. Compare the fitness of the mutant bug to the others. Was this particular mutation
helpful, harmful, or neutral?
d. Press Play and observe the predation in this generation. Did the mutant bug survive?
Remember that a small fitness difference will mean a slight change in the probability of
getting eaten, so it is quite possible that more fit bugs will be eaten and less fit bugs will
survive.
4. Continue the simulation for several generations. Click Pause when there is a variety of bug
colors. (Note: By increasing the Sim. Speed one step, you can view a quicker version of the
animation.) At this point, you should find a range of fitness values. (If not, play a few more
gereations or click Reset and try again.) Make sure the paretns are still visible. If they are not,
run an additional generation at the minimum speed, and click Pause.
a. What is the average fitness now? Has it imporved much so far?
b. Mosue over the parent bugs to see their genotypes. Try to find a parent pair that has
four different chromosomes. (If you can’t find any, play a few more generations and try
again.)
c. In your notes, record the genotypes of the two parents. Label the first parent’s
chromosomes “1” and “2” and the second parent’s chromosomes “3” and “4”.
d. Did any mutations occur in this set of offspring? If so, in which chromosome did the
mutation occur?
e. Now record the genotype of each offspring form the set you chose. Can you identify
chromosomes 1, 2, 3, and 4 in the offspring? Can a single offspring bug inherit both
chromosomes 1 and 2? Can a single offspring inherit 3 and 4? Explain why or why not?
f. Do all of the offspring look the same? Assuming no mutations, how many offspring
genotypes are possible from this parent pair?
g. Mutations are one source of variation in offspring. Based on what you have just seen,
what is a second source of variation?
h. Even if a bug with a helpful mutation survives predation and reproduces, the mutation
could disappear in the next generation. How could this happen?
5. In your notes, draw a diagram showing the 20 offspring insects (you do not have to color them
in). Mouse over each bug and note its fitness, and record the values on your diagram. With the
simulation set to its slowest speed, click Play, observe the results of predation, and click Pause.
Cross out the bugs that were eaten on your diagram.
a. Did all of the fittest bugs survive?
b. Were all of the least fit bugs eaten?
c. Was selection “fair” in this generation? Or did some bugs survive that shouldn’t have
based on their fitness? Explain your answer.
d. Based on the predation you observed, were the fittest bugs more likely to survive? How
can you tell?
e. While selection in a single gereation may seem random, what do you think will happen
to the bug population after many generations?
6. Increase the simulation speed, and Click Play. Observe the color of the bugs and the average
fitness value. Click Pause when the fitness and color stabilizes.
a. How well do the bugs blend into the background now? Are they easy to spot?
b. What is the average fitness value now? What is the maximum fitness of these bugs?
c. What genotype seems to be ideal for the background you have chosen?
d. About how many generations did it take for the bugs to adapt to their surroundings?
e. How can random mutations lead to adaption?
f.
Would the bug population have been able to adapt to the background without any
mutations occurring at all? Explain you reasoning.
7. Darwin’s theory of evolution by natural selection has four components:
i. Overproduction—More organisms are born than will survive and reproduce.
ii. Competition—Organisms compete for resources and to wavid being killed.
iii. Variation—Not all organisms are the same.
iv. Selection—Based on their traits, some organisms are more likely to survive and
reproduce than others.
a. Explain how each of the four parts of Darwins’s theory is represented in this simulation.
If possible, discuss your answer with your classmates and teacher.
b. Explain how an organism like the leaf katydid could have evolved from a common
grasshopper. Be sure to reference the four parts of the theory of natural selection in
your answer. Again, if possible, discuss your answer with your classmates and teacher.