Application Questions And Problems

10. Joe is color-blind. His mother and father both have normal vision, but his mother's father (Joe's maternal grandfather) is color-blind. All Joe's other grandparents have normal color vision. Joe has three sisters — Patty, Betsy, and Lora — all with normal color vision. Joe's oldest sister, Patty, is married to a man with normal color vision; they have two children, a 9-year old color-blind boy and a 4-year-old girl with normal color vision.

(a) Using correct symbols and labels, draw a pedigree of Joe's family.

(b) What is the most likely mode of inheritance for color blindness in Joe's family?

(c) If Joe marries a woman who has no family history of color blindness, what is the probability that their first child will be a color-blind boy?

(d) If Joe marries a woman who is a carrier of the color-blind allele, what is the probability that their first child will be a color-blind boy?

(e) If Patty and her husband have another child, what is the probability that the child will be a color-blind boy?

11. A man with a specific unusual genetic trait marries an unaffected woman and they have four children. Pedigrees of this family are shown in parts a through e, but the presence or absence of the trait in the children is not indicated. For each type of inheritance, indicate how many children of each sex are expected to express the trait by filling in the appropriate circles and squares. Assume that the trait is rare and fully penetrant.

(a) Autosomal recessive trait

(b) Autosomal dominant trait

(c) X-linked recessive trait

(d) X-linked dominant trait

(e) Y-linked trait

* 12. For each of the following pedigrees, give the most likely mode of inheritance, assuming that the trait is rare. Carefully explain your reasoning.

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