Download HW-Monohybrid Practice Seals and Guthry WS

Biology I
Unit II: Genetics
Chapter 11: Introduction to Genetics
Monohybrid Practice
Name: ________________________
Date: _______________ Hour: ____
Monohybrid Punnett Square Practice
In seals, the gene for the length of whiskers has 2 alleles. The dominant allele (W) codes for long
whiskers and the recessive allele (w) codes for short whiskers.

Write the genotype for the following:
o Homozygous long whiskers = _____
o Homozygous dominant = ______
o Heterozygous long whiskers = _____
o Homozygous recessive = ______
o Short whiskers = ______
o Heterozygous = ______
Mate two heterozygous seals.
Genotypic ratio:
Key:
Phenotypic ratio:
Cross:
1. What is the genotype of both parents?
_____________
2. What is the phenotype of both parents?
_____________
Suppose two long-whiskered seals are mated. The female is homozygous dominant, and the male
is heterozygous. Cross them.
Key:
Genotypic ratio:
Cross:
Phenotypic ratio:
3. What are the genotypes of both parents?
Female __________ Male ___________
4. What percentage of the offspring would be expected to have short whiskers from this
mating? ____________
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Mate a male seal that is true breeding for long whiskers with a female with short whiskers.
Key:
Genotypic ratio:
Cross:
Phenotypic ratio:
5. What are the genotypes of both parents?
Female __________ Male ___________
Silkworms have a dominant allele (C) for yellow cocoons and a recessive allele (c) for white
cocoons.
6. What is the genotype for homozygous dominant? _______________
7. What is the genotype for homozygous recessive? _______________
8. What is the genotype for heterozygous? _______________
9. What is the phenotype for homozygous dominant? _______________
10. What is the phenotype for homozygous recessive? _______________
11. What is the phenotype for heterozygous? _______________
Perform a cross of a homozygous dominant male and a homozygous recessive female.
Key:
Genotypic ratio:
Phenotypic ratio:
Cross:
12. What percent of the offspring will make white cocoons? _____________
13. What probability of the offspring will make yellow cocoons? _____________
14. What probability of the offspring will carry the gene for making white cocoons while
making yellow cocoons? _____________
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German Shepard dogs are usually black with tan (B). Sometimes there will be one that is born
white (b). White is a recessive trait, so a dog has to be homozygous recessive to be born white.
Mate a black and tan homozygous male with a black and tan heterozygous female.
Key:
Genotypic ratio:
Cross:
Phenotypic ratio:
15. What percentage of the puppies will be white? ________________
16. What percentage of the puppies will have only one allele for white color? ____________
Mate a black and tan heterozygous male with a white female.
Key:
Genotypic ratio:
Cross:
Phenotypic ratio:
17. What probability of the puppies will be white? ________________
18. What probability of the puppies will have only one allele for white color? ____________
Many humans have genetic disorders. Cystic Fibrosis is a recessive genetic disease. This means
that only those individuals with two recessive alleles (ff) will be afflicted with the disease,
however heterozygous individuals would carry the disease and possibly pass it to their offspring.
Suppose now that a woman that is a carrier for Cystic Fibrosis marries a man that does not have
or carry the disease. Cross this couple.
Key:
Genotypic ratio:
Cross:
Phenotypic ratio:
19. What percentage of their children could have the disease? _______________
20. What percentage would be carriers of the disease? ______ What is the genotype? ______
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Huntington’s disease is also a genetic disorder. It is caused by a dominant allele. A person with
Huntington’s disease often does not show symptoms until they are older and have had children.
There was a country and western singer from the 40’s and 50’s named Woody Guthrie. He sold
many records and became very famous. Though he was often on the road performing, he did find
the time to get married and have children. But fame was not without misfortune. Woody was
diagnosed with Huntington’s disease, which he inherited from his mother. His father did not
have the disease. Huntington’s disease robbed Woody his health, talent, and abilities. He spent
13 years in hospitals before his death in 1967.
Arlo Guthrie is the oldest son of Woody. He inherited his father’s talent for music. He started
performing in public at age 13. In the late 60’s he became very famous and performed at many
rock festivals.
But, is musical talent the only thing that Arlo inherited from his father? What is the chance Arlo
will have Huntington’s disease? Arlo’s mom does not have the disease.
21. What would be Woody’s genotype? __________________
22. What would be Arlo’s mom’s genotype? __________________
23. Do a punnett square to see what Arlo’s possible genotypes are.
Genotypic ratio:
Key:
Phenotypic ratio:
Cross:
24. What is the probability Arlo has Huntington’s disease? __________________
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