Download Canine Coat Color

Name ________________________________ Class _______ Date _________________
Canine Coat Color
Use the virtual Genetics lab room to
determine the pattern of inheritance of coat
color in Labrador retrievers.
Lab Bench Used
In Labrador retrievers, or Labs, coat color is a polygenic trait. This means that more than one
gene determines the color of a Lab’s fur. A Lab can have black or brown coat pigments, or it can
have no fur pigment, which causes the fur to appear yellow. In this virtual genetics lab activity,
you will run different crosses to determine the pattern of inheritance of this polygenic trait.
Enter the Virtual Bio Lab and select the title of this lab activity from the “Heredity”
menu on the whiteboard. You will be taken to the virtual Genetics lab room.
Part A: A Polygenic Trait
Select “Dog, Domestic” from the Species Selector. Select “Coat Color” as the trait
you will study. Look at your options in the “Set Alleles” box. Notice that this trait is
determined by alleles two different loci (plural of locus), or locations on the
chromosome. Coat color is therefore a polygenic trait.
1. What are the different allele possibilities for each of the two loci?
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Before determining dominant-recessive relationships of each set of alleles, test to see
whether one locus is dominant over the other. To test the dominance between the two
loci, cross the parents using their default genotype settings—both parents are
homozygous for black coat and no pigment. Cross the parents enough times to
produce 50 puppies.
2. What color puppies do these parents (both homozygous for black coat and no
pigment) produce? What do these results tell you?
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Reset the lab and set up a new cross. This time, set the female’s Locus 2 alleles to be
heterozygous (one allele for “Pigment” and one for “No pigment.”) Set Locus 1 to be
homozygous black for both the male and female.
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Virtual Bio Lab
1
Heredity:
Canine Coat Color
Name ________________________________ Class _______ Date _________________
3. What happens when you cross these parents? What do these results suggest about
the inheritance pattern of the Locus 2 alleles? Explain your reasoning.
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4. Roll over the names of the two parents in the “Results” box. How do their
phenotypes make sense in light of their genotypes and the inheritance pattern of
the “Pigment” and “No pigment” alleles?
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Part B: Black vs. Brown
Reset the lab. Set up a cross to determine how the Locus 1 alleles (black vs. brown)
interact. First, set both parents’ Locus 2 alleles as homozygous for pigment. It is up
to you to decide how to set the Locus 1 alleles so you will find which one, if any, is
dominant and which is recessive.
5. Describe your crosses and findings.
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Virtual Bio Lab
2
Heredity:
Canine Coat Color
Name ________________________________ Class _______ Date _________________
6. Fill in the Punnett square below to show the results of a cross between a yellow female and
a brown male that is heterozygous for pigment. Set the parental genotypes using P and p for
the Locus 2 alleles. What percentage of the yellow female's puppies would share her yellow
coat color?
Yellow Female
Brown
Male
7. Why wasn’t it necessary to build a 16-cell Punnett square to answer Question 6?
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8. If both parents are heterozygous in both of the loci that are involved in coat color, what
coat colors should be expressed in a very large litter of puppies? Explain your
reasoning.
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9. Run the cross as described in Question 8 to see if the results match your prediction.
Describe your results.
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Virtual Bio Lab
3
Heredity:
Canine Coat Color
Name ________________________________ Class _______ Date _________________
10. Think about the pair of dogs you just crossed. Given their appearance and the offspring they
produced, why might breeding Labrador retrievers be more challenging than some people
imagine? How does knowing the parents’ genotypes make it easier?
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Part C: Breeding Dogs
Imagine you are a dog breeder. You have a female black Lab that was produced by a brown
mother and an unknown father. You want to find a mate for your dog so she'll produce brown
puppies. What genotype would you need her mate to have in order to guarantee that some of the
puppies will be brown? Work through the following questions to find the answer. Experiment
within the virtual Genetics lab to help figure out the answers.
11. For the Locus 1 gene, what is the genotype of your black dog? How do you know?
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12. Did your dog's father have a black coat?
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13. To have the best chance of producing brown puppies, what is the ideal phenotype of your
dog's potential mate? Explain.
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Virtual Bio Lab
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Heredity:
Canine Coat Color
Name ________________________________ Class _______ Date _________________
14. Is there any chance that some of your dog's offspring will be yellow?
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15. If your dog is heterozygous for both genes, and she mates with a brown male, at minimum,
what percentage of her puppies should you expect to be brown? What about at maximum?
Explain.
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Virtual Bio Lab
5
Heredity:
Canine Coat Color