Problem Set – Mendelian Genetics Questions

Mendelian Genetics Questions

Instructions: Consult your textbook if necessary.  These are practice questions; you do not have to turn in your answers.

1. For each of the following genotypes of Mendel’s pea plants, give the genotypes of all the different gametes it could produce:  RR;  Yy;  RrYY;  RrGg;  RrGgYy;  RRggYY.
2. A pea plant with yellow seeds was crossed to a pea plant with green seeds, and some of the offspring were green.  What was the genotype of the parent plant with yellow seeds?
3. What fraction of the offspring in Question 2 had green seeds?
4. If the parent plant with yellow seeds in Question 2 was self-fertilized, what fraction of the offspring would have green seeds?
5. Could a pea plant with white flowers and wrinkled seeds produce any offspring with purple flowers or round seeds if it was self-fertilized?  Explain.
6. What about a pea plant with purple flowers and round seeds.  Could it produce offspring with white flowers or wrinkled seeds if it was self-fertilized?  Explain.
7. What fraction of the offspring of the plant self-fertilized in Question 6 would have both purple flowers and round seeds?
8. What fraction of the offspring of the plant self-fertilized in Question 6 would have both white flowers and wrinkled seeds?
9. Which of Mendel’s principles do you use to answer Questions 2,3, and 4?
10. Which of Mendel’s principles do you use to answer Questions 7 and 8?
11. What term means “a backcross to a homozygous recessive”?
12. What term means “a heritable trait”?
13. What term means “a variant of a heritable trait”?
14. Suppose you cross a plant with purple flowers and round seeds to a plant with purple flowers and wrinkled seeds.  You get both purple and white flowers and both round and wrinkled seeds in the offspring.  What are the genotypes of each parent plant?
15. Diagram the cross in Question 14 using a Punnett square.  What are the expected phenotypic ratios and genotypic ratios in the offspring?
16. Put the gene for round seeds on one chromosome and the gene for wrinkled seeds on its homologous chromosome and show how meiosis is the basis for the Principle of Segregation.
17. Show how the XX-XY mechanism of sex determination found in mammals potentially can produce equal numbers of males and females.
18. In humans, red hair is recessive to dark hair.  Two dark-haired parents have a red-haired son.  What are the genotypes of the parents?
19. What are the chances of the dark-haired parents in Question 18 having a red-haired child?
20. Widow’s peak in humans is dominant to straight hairline.  Cross a person who has a widow’s peak (whose father had a straight hairline) with a person with a straight hairline.  What are the probabilities of the possible genotypes of their children?
21. In humans, brown eyes is usually dominant over blue eyes.  If a blue-eyed man is crossed with a brown-eyed woman (whose father was blue-eyed), what are the probabilities of the possible phenotypes of their children?
22. Using the information in Questions 18 and 21, cross a person who has red hair and blue eyes with someone with dark hair and brown eyes (whose father had red hair and blue eyes).  What is the chance that one of their children will have both dark hair and blue eyes?