121 Critical Thinking Questions

22. Choose one of the following two questions (option a or option b):

• Option a) Describe one of the reasons why the garden pea was an excellent choice of model system for studying inheritance.
• Option b) What organism would you choose as a model system for studying inheritance? Name one reason for choosing this organism.

23. How would you perform a reciprocal cross for the characteristic of stem height in the garden pea?

24. Mendel performs a cross using a true-breeding pea plant with round, yellow seeds and a true-breeding pea plant with green, wrinkled seeds. What is the probability that offspring will have green, round seeds? Calculate the probability for the F₁ and F₂ generations.

25. Choose one of the following two questions (option a or option b):

• Option a) Calculate the probability of selecting a heart or a face card from a standard deck of cards. Is this outcome more or less likely than selecting a heart suit face card?
• Option b) A computer software can generate either random numbers or either random letters. Calculate the probability of the software selecting the number combination 77 and calculate the probability selecting the letter combination ZB. Which combination is less likely to occur?

26. The gene for flower position in pea plants exists as axial or terminal alleles. Given that axial is dominant to terminal, list all of the possible F₁ and F₂ genotypes and phenotypes from a cross involving parents that are homozygous for each trait. Express genotypes with conventional genetic abbreviations.

27. Use a Punnett square to predict the offspring in a cross between a dwarf pea plant (homozygous recessive) and a tall pea plant (heterozygous). What is the phenotypic ratio of the offspring?

28. Can a human male be a carrier of red-green color blindness?

29. Why is it more efficient to perform a test cross with a homozygous recessive donor than a homozygous dominant donor? How could the same information still be found with a homozygous dominant donor?

30. Use the probability method to calculate the genotypes and genotypic proportions of a cross between AABBCc and Aabbcc parents.

31. Explain epistasis in terms of its Greek-language roots (“standing upon”).

32. In Section 12.3, “Laws of Inheritance,” an example of epistasis was given for the summer squash. Cross white WwYy heterozygotes to prove the phenotypic ratio of 12 white:3 yellow:1 green that was given in the text.

33. People with trisomy 21 develop Down’s syndrome. What law of Mendelian inheritance is violated in this disease? What is the most likely way this occurs?

34. A heterozygous pea plant produces violet flowers and yellow, round seeds. Describe the expected genotypes of the gametes produced by Mendelian inheritance. If all three genes are found on the same arm of one chromosome, should a scientist predict that inheritance patterns will follow Mendelian genetics?