Genetics Problems

Here are some more problems to practice your knowledge of genetics!
(Do them just for exam practice, they will not be turned in or graded)

Practice Problems
Tip: Remember that for any gene or trait,
'homozygous dominant' means AA,
'heterozygous' (also called a carrier) means Aa and
'homozygous recessive' means aa


1. A woman is heterozygous for Tay-Sachs. What are the chances of her giving birth to a child with Tay-Sachs (a homozygous recessive disorder) if the father is normal (homozygous dominant?) What are the chances of giving birth to a carrier like herself?



2. Both you and your sister have attached earlobes, yet your parents have unattached ones. Unattached earlobes are dominant over attached. Give the genotypes of you, your sister, and your parents.



3. Parents who are carriers for have sickle-cell disease produce a child who has sickle-cell disease. What are the chances that their next child will have sickle-cell disease?



4. A woman with PKU (kk) marries a man who is genotypically normal (KK). Which answer below best describes the chances that their child will: be genotypically normal (KK), be a carrier for PKU (Kk), or have the disease PKU (kk) ?



5. If both your parents have a continuous hairline (cc), what best describes your possibilities for hairlines?



6. Both Dick and Jane have freckles (dominant) and attached earlobes (recessive). Six of their children do not have freckles. What are the chances that their next child will have freckles and attached earlobes?



7. In a dihybrid cross of a heterozygous pea plant with purple flowers and round seeds (PpRr), what is the probability that

a) a white-flowered pea plant with round seeds will be produced?_______________

b) a purple-flowered pea plant with round seeds will be produced? ______________

c) a white-flowered pea plant with wrinkled seeds will be produced? _____________

d) a purple-flowered pea plant with wrinkled seeds will be produced? _____________

e) the genotype PpRr will result? ______________

f) the genotype ppRr will result? ______________

g) the genotype PpRR will result? ______________

h) the genotype ppRr will result? ______________

8. In a trihybrid cross of a tall, purple-flowered pea plant with round seeds (TtPpRr) with a tall, white-flowered pea plant with wrinkled seeds (Ttpprr), what is the probability:

a) that a tall, white-flowered plant with wrinkled seeds will be produced?__________

b) that a short, purple-flowered plant with round seeds will be produced? __________

c) that a short, white-flowered plant with wrinkled seeds will be produced? ________

d) that a tall, purple-flowered plant with round seeds will be produced? ___________

e) that a tall, white-flowered plant with round seeds will be produced?____________

9. A woman is heterozygous for polydactyly and has 6 fingers on each hand (polydactyly is a dominant trait). What are the chances of her giving birth to a child with polydactyly if the father is normal (homozygous recessive)?





10. In Labrador retriever dogs, the gene B (dominant) produces black coat color (BB or Bb; black Lab), with the homozygous recessive condition (bb) producing brown Lab. The dominant epistatic gene E controls the presence of coat color. The homozygous recessive ee condition prevents the deposition of coat color, resulting in a golden Lab (regardless of whether the coat color is black - BB or Bb or brown – bb). Give the probability of the following crosses:

11. Both a husband and wife have normal vision but their son is color blind. What are the likely genotypes of the boy’s parents? Of the boy?