CP Bio
Name___________________________________________
Scorese
Date_____
Exploration Guide: Mouse Genetics Gizmo(One Trait)
The field of genetics is one of the most rapidly advancing branches of science, and many
of its discoveries will have a profound effect on our lives. In this Gizmo™, you will be
introduced to the basic ideas of genetics. By looking at just one trait, fur color, you will
be able to see how genes are passed from parents to offspring. Along the way, you will
rediscover the laws of inheritance that Gregor Mendel determined 150 years ago.
Observing Patterns of Inheritance
In this activity, you will experiment with different combinations of mouse parents to see
how fur color is passed to their offspring.
1. On the Gizmo, drag a black mouse over the Parent 1 label in the purple breeding
cage at the top of the tree diagram. Then, drag a second black mouse over the Parent 2
label. These mice will be the parents in your first experiment.
A. What color offspring do you expect to result from these parents? ___________
Click Breed and observe the offspring. Was your hypothesis correct?
B. Click Breed several more times to generate additional litters from the same
parents. Did all of the offspring have the same fur color? _______________
2. Click Clear, and then drag two white mice to the breeding cage. Click Breed several
times to generate litters from the white-fur parents. What pattern did you observe in the
offspring?
3. Click Clear, and then drag a white mouse and a black mouse into the breeding cage.
A. With a black-fur and a white-fur parent, what are the possible colors for the
offspring? Write down what you expect the offspring to look like.
B. Click Breed. What did the offspring look like? Did this agree with your
prediction?
C. Click Breed several more times to confirm your results. Were any of the
offspring different? Explain your results.
D. Drag two of the offspring mice into the Holding Cages at the bottom of the
Gizmo for use in future experiments.
4. Experiment with a variety of other parent combinations, using the "Pure" mice at left
and the mice in the Holding cages. Try to explain any interesting patterns you find.
A. What combinations of parents give rise to only white-fur offspring?
B. What combinations of parents give rise to only black-fur offspring?
1
C. Are there any combinations that give rise to both black and white-fur offspring?
Predicting Genetic Crosses
In this activity, you will learn how genes are passed down from parents to their offspring.
1. On the Gizmo, turn on Show genotype. In general, every type of gene has two
versions, called alleles. In this example, the allele for black fur is F and the allele for
white fur is f. The genotype is the combination of alleles that an organism has. The
phenotype is what the organism looks like. For example, a mouse with the genotype FF
will have the phenotype black fur. Drag a pure black mouse and a pure white mouse into
the breeding cage.
A. Move the cursor over the black mouse. What is the genotype of a pure black
mouse?
B. Move the cursor over the white mouse. What is the genotype of a pure white
mouse?
2.Usually, one allele is called dominant, which means that an organism will always have
that trait if the dominant allele is present. The other allele is called recessive, which
means that its effects are masked when the dominant allele is present. Click Breed.
Which allele do you think is dominant in this case? ________Which allele is recessive?
Move the cursor over one of the offspring to view its genotype. What allele did this
mouse inherit from its black-fur parent? _______What allele did the mouse inherit from
its white-fur parent? ________What color is the mouse?___________
3. An organism that contains two different alleles (such as Ff) is called heterozygous.
One that has two of the same alleles (FF or ff) is called homozygous. Are the offspring of
this pair heterozygous or homozygous?________________________ What color are the
heterozygous mice? _________________________________
4. Drag two of the offspring into the Holding Cages and click Clear. Then, drag the two
mice from the Holding Cages into the breeding cage.
A. Move the cursor over the first parent and observe its genotype. What alleles
could this parent pass on to its offspring?
B. Move the cursor over the second parent and observe. What alleles could this
parent pass on?
5. To model the possible allele combinations in the offspring, geneticists use a diagram
called a Punnett Square. Draw a Punnett Square below that shows the cross between two
heterozygous parents.
Look at the four offspring genotypes in your Punnett Square. According to this, what
percentage of the offspring should be white? What percentage should be black?
2
6. Select Show Statistics and click Breed. Keep clicking Breed until you have generated
100 offspring. How do the numbers of black and white offspring compare to your
predicted percentages?
7. When you are finished, drag a heterozygous mouse back into a Holding Cage and click
Clear.
8. Drag a pure white mouse and the heterozygous mouse from the Holding Cage into the
breeding cage.
A. Create a Punnett Square for a heterozygous black parent (Ff) and a homozygous
white parent (ff).
Based on your Punnett Square, what are the predicted percentages of black and
white offspring?
9. Click Breed until you have generated 100 offspring. How close were your results to the
predicted percentages?
10. Experiment with another combination of your choice. In each case, create a Punnett
Square to predict the percentages of black and white offspring before running your
experiment. How did the actual results compare to the predicted?
11. You may have noticed that the predicted percentages do not exactly match the results.
It is a basic rule of probability that the results do not always match predictions. For
example, even though there is a 50% chance of having a boy or a girl, there are lots of
families that have several sons and no daughters, or several daughters and no sons. If you
have the time and patience, try breeding a pure white and a heterozygous black mouse
until you have 1,000 offspring. As the sample size increases, do the results get closer to
the predicted percentages? Why do you think this is?
3
Exploration Guide: Mouse Genetics Gizmo(Two Traits): Now
we can “kick it up a notch!”
**Close the first gizmo and open up the second gizmo that is designed for Two Traits.**
When multiple traits are considered, the number of possible offspring phenotypes
increases exponentially. With two traits there are four possible phenotypes. With three
traits there are eight possible phenotypes. Considering that humans pass on thousands of
genes to their children, it is no wonder that every person is unique!
Patterns of Inheritance
In this activity, you will explore patterns of inheritance for two traits — fur color and
eye color.
1. In the Gizmo™, parent mice can be dragged into the purple breeding cage at the top of
the diagram. Drag two "pure" black fur/black eye mice into the breeding cage, and click
Breed.
A. Do all of the offspring look the same as the parents?_________________
B. Turn on the Show genotype checkbox, and point to a mouse to see its
genotype. What is the genotype of the parent mice? _________________What is
the genotype of each offspring mouse?____________________________
Because these mice have identical alleles for fur color (FF) and identical alleles
for eye color (EE), they are homozygous for both traits, and all offspring are
identical.
2. Point to each of the other "pure" mice on the left side of the Gizmo and observe their
genotypes.
A. What is the (single letter) symbol for the black fur allele? _____________
What is the symbol for white fur? ____________
B. What is the allele symbol for black eyes? ___________
What is the allele symbol for red eyes?____________
3. Click Clear, and then drag a pure black fur/black eye mouse (FF EE) and a pure white
fur/red eye mouse (ff ee) into the breeding cage. (Do not breed them yet.)
A. What do you expect the offspring to look like? _________________
B. What genotype(s) do you expect to see in the offspring?
_____________________
C. Click Breed several times to check your predictions. What phenotypes do you
see in the offspring? __________________________
What genotypes do you see?
D. The offspring you see are heterozygous for each trait, meaning their two alleles
for each trait are different. Based on their appearance, which alleles are dominant?
E. Drag two of the offspring into the Holding Cages below, for use in the next
experiment.
4. Click Clear, and drag the two mice from the Holding Cages into the breeding cage
above. Turn on the Show statistics checkbox, and click Breed.
4
A. Are all of the offspring the same?
What offspring phenotypes appear in the first litter?
B. Point to several of the offspring. What offspring genotypes do you see?
C. Click Breed several more times. What offspring phenotypes are most common?
Least common?
D. Observe the genotypes of some of the different offspring. Is there more than one
genotype that codes for some phenotypes? For example, how many genotypes can
code for a mouse with black fur and black eyes? What are they?
How many genotypes can code for a mouse with white fur and red eyes? What are
they?
Independent Assortment
When two events are independent, the probability of both events occurring is the product
of the probabilities. For example, the probability of having a flipped coin come up heads
twice in a row is 1/2 • 1/2 = 1/4. OR (.5 X.5 =.25) As long as two traits are inherited
independently, you can use the same rule to determine the probabilities of offspring
genotypes and phenotypes. This method of determining probability is called the Product
Method.
1. Click Clear, and drag a pure black fur/black eye mouse and a pure white fur/black
eye mouse into the breeding cage. Click Breed, and then drag two of the offspring into
the Holding Cages. Click Clear again, and then drag the two offspring from the Holding
Cages to the breeding cage. (Check that both parents now have identical Ff EE
genotypes.)
A. Click Breed repeatedly until 100 offspring are generated. What is the percentage
of offspring with black fur? ______________White fur? ______________
B. What is the theoretical probability that an offspring mouse will have black fur?
White fur? See your results from the One Trait part of this lab.
C. Were your experimental results close to the theoretical probabilities? Were they
an exact match? Explain why you think this is so.
2. Click Clear, and then breed a pure black fur/black eye mouse to a pure black fur/red
eye mouse. As you did before, place two of the offspring into the Holding Cages, click
Clear, and then move the two offspring mice from the Holding Cages to the breeding
cage. Both parents should now have the genotype FF Ee.
A. Complete a Punnett Square to find the theoretical probabilities of black-eyed
offspring, and of red-eyed offspring (ignore fur color).
5
B. Out of 100 offspring, how many do you expect to have black eyes? _________
C. Use the Gizmo to test your prediction. What were the experimental results?
Were these results reasonably close to what was predicted?
3. Now suppose you bred two mice with the genotype Ff Ee. (As you did in the first
activity of this guide, you can set up this situation by breeding a black fur, black eye
mouse to a white fur, red eye mouse, placing two offspring into Holding Cages, and then
breeding these two mice.)
A. Ignoring eye color, what is the theoretical probability of inheriting black fur?
B. Ignoring fur color, what is the theoretical probability of inheriting black eyes?
C. Assuming the inheritance of each trait is independent, what is the probability of
inheriting black fur and black eyes? (Convert probability to decimal and multiply)
D. Using the same reasoning, what is the probability of inheriting
Black fur and red eyes? _________________
White fur and red eyes? _________________
White fur and black eyes?________________
E. Of 160 hypothetical offspring, how many would you expect to have each
phenotype? (Multiply your probabilities(as decimals) from above by 160)
Black fur/black eyes: _______________
Black fur/red eyes: _______________
White fur/black eyes: _____________
White fur/red eyes: ________________
7. Click Breed, and generate 160 offspring. How close were the results to your
predictions?
If the results of breeding experiments are reasonably close to their predicted values, it
confirms that the traits are inherited independently. This is known as Mendel's Law of
Independent Assortment.
8. A second way to predict inheritance of two traits is with an expanded Punnett Square
Method. In this case, each parent contributes two alleles to each offspring, one for fur
color and one for eye color. Fill in the Punnett Square below for a cross between two
heterozygous black fur and black eyes
A. Of the 16 offspring represented in the Punnett Square, how many have black
fur and black eyes? ______________________
B. How many have black fur and red eyes?
C. White fur and black eyes?
D. White fur and red eyes?
E. How do these probabilities compare to what you found before with the
previous Product Method? Agree? Explain.
6
5. Investigate the following parent combinations. In each case, use either method to
predict the fraction or percentage of each offspring phenotype. Then, use the Gizmo to
check your answer.
Ff Ee and ff ee
Possible Phenotypes
Expected Phenotypes
Observed Phenotypes
Black fur/black eyes
Black fur/red eyes
White fur/black eyes
White fur/red eyes
Ff EE and Ff ee
Possible Phenotypes
Black fur/black eyes
Black fur/red eyes
White fur/black eyes
White fur/red eyes
Ff ee and Ff Ee
Possible Phenotypes
Black fur/black eyes
Black fur/red eyes
White fur/black eyes
White fur/red eyes
Expected Phenotypes
Observed Phenotypes
Expected Phenotypes
Observed Phenotypes
© 2009 ExploreLearning http://www.explorelearning.com/
7