Question

Excess Thyroxin-binding Globulin (ETG) is a thyroid disorder that is inherited with the X-linked dominant allele E. The X-linked recessive allele e does not contribute to ETG. Short index finger, where the index finger is shorter than the ring finger, is a sex-influenced autosomal trait that is dominant in males and recessive in females. Let allele S1 be for short index fingers and allele S2 be for long index fingers. The inheritance pattern for this trait is shown in the following table:

Genotype	Trait for Male Child	Trait for Female Child
S1 S1	Short Index Fingers	Short Index Fingers
S1 S2	Short Index Fingers	Long Index Fingers
S2 S2	Long Index Fingers	Long Index Fingers

a. Henry has ETG and long index fingers. His wife Harriet has ETG and short index fingers. Harriet’s father does not have ETG. Out of 4 children born to Henry and Harriet, what is the probability that 3 will be sons with short index fingers who do not have ETG?

b. For Henry and Harriet, what is the probability that their first child will be a daughter with long index fingers who has ETG and their second child will be a son with short index fingers who has ETG and their third child will be a son with short index fingers who does not have ETG?

c. Maurice has short index fingers but does not have ETG. Maurice’s wife Marilyn has long index fingers and ETG. Maurice’s father has long index fingers. Marilyn’s mother has short index fingers and does not have ETG. Out of 3 children born to Maurice and Marilyn, what is the probability that at least one will be a son with ETG and short index fingers?

d. What is the probability that the first child born to Maurice and Marilyn will be either a daughter with long index fingers and no ETG or a son with short index fingers and no ETG?

Answer 1