Pedigree Analysis Question Paper

Unit 2, Chapter 1: Principles of Inheritance and Variation

Total Questions: 50

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Section A: Multiple Choice Questions (20 Questions)

Instructions: Choose the best answer for each question.

1. Which of the following is a key feature of an autosomal dominant inheritance pattern?

   • a. The trait skips generations.
   • b. The trait appears in every generation.
   • c. More males are affected than females.
   • d. Affected individuals have unaffected parents.

2. In an autosomal recessive inheritance pattern, what is the approximate percentage of offspring affected when two carrier parents mate?

   • a. 100%
   • b. 75%
   • c. 50%
   • d. 25%

3. What is a characteristic feature of X-linked dominant inheritance?

   • a. Affected fathers pass the trait to all their sons.
   • b. Affected fathers pass the trait to all their daughters.
   • c. The trait skips generations.
   • d. More males are affected than females.

4. In X-linked recessive inheritance, who are usually the carriers of the trait?

   • a. Affected males
   • b. Unaffected males
   • c. Affected females
   • d. Unaffected females (daughters of affected fathers)

5. If a trait appears in every generation and affects both males and females equally, what is the most likely mode of inheritance?

   • a. Autosomal recessive
   • b. X-linked recessive
   • c. Autosomal dominant
   • d. X-linked dominant

6. What does "consanguinity" in a pedigree chart suggest?

   • a. A mating between unrelated individuals.
   • b. A high probability of a dominant trait.
   • c. A mating between relatives, common in autosomal recessive pedigrees.
   • d. A new mutation.

7. In X-linked dominant inheritance, if an affected mother passes the trait, what is the probability of her offspring being affected?

   • a. 100% of daughters
   • b. 100% of sons
   • c. 50% of offspring, regardless of sex
   • d. 25% of offspring

8. What is the term for an individual who is heterozygous for a recessive trait but does not show the phenotype?

   • a. Affected
   • b. Carrier
   • c. Homozygous
   • d. Hemizygous

9. Which inheritance pattern shows no male-to-male transmission?

   • a. Autosomal dominant
   • b. Autosomal recessive
   • c. X-linked (both dominant and recessive)
   • d. Y-linked

10. If an unaffected individual has an allele for a dominant trait, what would be the outcome?

    • a. They would be a carrier.
    • b. They would be unaffected.
    • c. They would be affected.
    • d. This scenario is not possible with complete penetrance.

11. In a pedigree, what does a horizontal line connecting a square and a circle represent?

    • a. Siblings
    • b. Mating
    • c. Offspring
    • d. Deceased individuals

12. What is the genotype of an individual affected by an autosomal recessive trait?

    • a. AA
    • b. Aa
    • c. aa
    • d. XaY

13. If an affected male has an X-linked recessive trait, from whom did he inherit the allele?

    • a. His father
    • b. His mother
    • c. Both parents
    • d. A new mutation

14. What is the key feature of Y-linked inheritance?

    • a. It affects only females.
    • b. It is passed from father to all sons.
    • c. It skips generations.
    • d. It is the most common form of inheritance.

15. In mitochondrial inheritance, who transmits the trait?

    • a. Only males
    • b. Only females to all their progeny
    • c. Both males and females equally
    • d. It is random.

16. What does a shaded symbol in a pedigree chart represent?

    • a. An unaffected individual
    • b. An affected individual
    • c. A deceased individual
    • d. A carrier

17. If a trait skips generations, which of the following is a possible mode of inheritance?

    • a. Autosomal dominant
    • b. X-linked dominant
    • c. Autosomal recessive
    • d. Y-linked

18. What is the term for the assumption that an individual marrying into a family with a rare trait is not a carrier?

    • a. Complete penetrance
    • b. Rare-in-population
    • c. Not-Y-linked
    • d. Hemizygous

19. In X-linked recessive inheritance, what is the status of all daughters of an affected father (assuming the mother is not a carrier)?

    • a. Affected
    • b. Unaffected and not carriers
    • c. Carriers
    • d. 50% are carriers

20. If an affected individual is heterozygous (Aa) for an autosomal dominant trait, what is the probability of passing the trait to their offspring?

    • a. 100%
    • b. 75%
    • c. 50%
    • d. 25%

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Section B: True/False Questions (10 Questions)

Instructions: State whether the following statements are true or false.

21. In autosomal dominant inheritance, affected individuals must have at least one affected parent.

22. X-linked recessive traits affect more females than males.

23. An unaffected individual can be a carrier of a dominant trait.

24. A father can transmit an X-linked gene to his son.

25. In autosomal recessive inheritance, two unaffected parents can have an affected child.

26. Y-linked traits are passed from a father to all his daughters.

27. Mitochondrial DNA is inherited from the father.

28. In X-linked dominant inheritance, affected fathers pass the trait to all their daughters.

29. A trait that appears in every generation is likely recessive.

30. Complete penetrance means that an individual with the disease-causing genotype will always express the phenotype.

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Section C: Short Answer Questions (10 Questions)

Instructions: Provide a brief answer to each question.

31. What are the three simplifying assumptions made in the provided pedigree problems?

32. What are the five key clues to remember when reasoning about pedigrees?

33. Explain the difference between autosomal and X-linked inheritance.

34. What is "criss-cross inheritance"?

35. Why are males more commonly affected by X-linked recessive traits?

36. How can you distinguish between autosomal dominant and X-linked dominant inheritance?

37. What is the genotype of a female carrier for an X-linked recessive trait?

38. What is the significance of assuming a trait is "rare-in-population"?

39. What are the key features of mitochondrial inheritance?

40. What is the genotype of an affected male with an X-linked dominant trait?

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Section D: Pedigree Analysis Problems (10 Questions)

Instructions: Analyze the following pedigrees and answer the questions.

Case 1:

[Pedigree chart would be displayed here]

41. What is the mode of inheritance shown in this pedigree?

42. What is the genotype of individual I-1?

43. What is the genotype of individual II-2?

Case 2:

[Pedigree chart would be displayed here]

44. What is the most likely mode of inheritance in this pedigree?

45. Can this be an X-linked dominant trait? Why or why not?

46. What is the genotype of individual III-1?

Case 3:

[Pedigree chart would be displayed here]

47. What is the mode of inheritance shown in this pedigree?

48. Why can't this be an autosomal recessive trait?

49. What is the genotype of individual II-5?

50. If individual III-2 marries an unaffected man, what is the probability of them having an affected child?

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Answer Key

Section A: Multiple Choice Questions

1. b. The trait appears in every generation.
2. d. 25%
3. b. Affected fathers pass the trait to all their daughters.
4. d. Unaffected females (daughters of affected fathers)
5. c. Autosomal dominant
6. c. A mating between relatives, common in autosomal recessive pedigrees.
7. c. 50% of offspring, regardless of sex
8. b. Carrier
9. c. X-linked (both dominant and recessive)
10. d. This scenario is not possible with complete penetrance.
11. b. Mating
12. c. aa
13. b. His mother
14. b. It is passed from father to all sons.
15. b. Only females to all their progeny
16. b. An affected individual
17. c. Autosomal recessive
18. b. Rare-in-population
19. c. Carriers
20. c. 50%

Section B: True/False Questions

21. True
22. False
23. False
24. False
25. True
26. False
27. False
28. True
29. False
30. True

Section C: Short Answer Questions

31. The three simplifying assumptions are:

    1. Complete Penetrance: Individuals with the genotype for a trait will always express the phenotype.
    2. Rare-in-Population: Individuals marrying into the pedigree are assumed not to be carriers of the rare trait.
    3. Not-Y-Linked: The traits in these problems are autosomal or X-linked, but not Y-linked.

32. The five key clues are:

    1. An unaffected individual cannot have any alleles of a dominant trait.
    2. Individuals marrying into the family are assumed to have no disease alleles.
    3. An unaffected individual can be a carrier of a recessive trait.
    4. When a trait is X-linked, a single recessive allele is sufficient for a male to be affected.
    5. A father transmits his allele of X-linked genes to his daughters, but not his sons.

33. Autosomal inheritance involves genes on the autosomes (non-sex chromosomes), and it affects males and females equally. X-linked inheritance involves genes on the X chromosome, leading to different patterns of inheritance in males and females.

34. Criss-cross inheritance is a pattern of inheritance where a trait is transmitted from father to daughter to grandson, or from mother to son to granddaughter. It is characteristic of X-linked recessive traits.

35. Males are more commonly affected by X-linked recessive traits because they are hemizygous (have only one X chromosome). A single recessive allele on the X chromosome will cause the trait to be expressed in males, whereas females need two recessive alleles to be affected.

36. To distinguish between autosomal dominant and X-linked dominant inheritance, look for the transmission from an affected father. In X-linked dominant inheritance, an affected father will pass the trait to all his daughters and none of his sons. In autosomal dominant inheritance, an affected father can pass the trait to both sons and daughters.

37. The genotype of a female carrier for an X-linked recessive trait is XAXa.

38. Assuming a trait is "rare-in-population" simplifies pedigree analysis by allowing us to assume that individuals marrying into the family are homozygous for the normal allele and are not carriers of the trait.

39. The key features of mitochondrial inheritance are:

    • The trait is passed from a mother to all of her offspring (both male and female)
    • Males do not transmit the trait to any of their children

40. The genotype of an affected male with an X-linked dominant trait is XaY.

Section D: Pedigree Analysis Problems

41. Case 1: The mode of inheritance is autosomal recessive.

42. Case 1: The genotype of individual I-1 is Aa (carrier).

43. Case 1: The genotype of individual II-2 is Aa (carrier).

44. Case 2: The most likely mode of inheritance is autosomal dominant.

45. Case 2: This cannot be an X-linked dominant trait because there is male-to-male transmission (e.g., individual I-1 passes the trait to his son II-5).

46. Case 2: The genotype of individual III-1 is aa (unaffected).

47. Case 3: The mode of inheritance is X-linked recessive.

48. Case 3: This cannot be an autosomal recessive trait because if it were, the affected female II-5 (aa) would have to have an affected father (aa), but her father I-1 is unaffected.

49. Case 3: The genotype of individual II-5 is XaXa (affected female).

50. Case 3: Individual III-2 is a carrier female (XAXa). If she marries an unaffected man (XAY), the probability of them having an affected child (XaY) is 25% (50% of sons).