Question

Joe is color blind. His mother and father 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. Take a picture and send it by email.
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?

Answer 1

Answer:

a. Using correct symbols and labels, draw a pedigree of Joe's family. Take a picture and send it by email.

The pedigree image is attached at the end.

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

X-linked recessive. Only males have the trait, and they inherit the trait from  

their mothers, who are carriers. The trait is never passed from father to son.

(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?

Barring a new mutation or nondisjunction, zero. Joe cannot pass his color-blind  X chromosome to his son.

(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?

The probability is ¼. There is ½ probability that their first child will be a boy,  

and there is an independent ½ probability that the first child will inherit the  

color-blind X chromosome from the carrier mother. ½(½) = ¼.