Question 1

Which of the following statements best explains why X-linked recessive traits, such as hemophilia, are more commonly observed in males than females?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will result in the trait being expressed.

Question 2

A man affected by an X-linked dominant disorder has children with a woman who does not carry the allele. What is the expected outcome for their children?

Accepted Answer

All daughters will be affected, all sons will be unaffected.

Question 3

Which pedigree pattern would you expect for a Y-linked trait?

Accepted Answer

Trait is seen only in males and is passed from father to all sons.

Question 4

A carrier female for an X-linked recessive trait (genotype $$X^AX^a) $$mates with a normal male ($$X^AY). $$What is the probability that their son will be affected by the trait?

Accepted Answer

$$\frac{1}{2}$$

Question 5

Which of the following is NOT a characteristic of X-linked recessive inheritance?

Accepted Answer

Trait is seen in every generation regardless of sex.

Question 6

A pedigree shows a trait present in every generation, affecting both males and females, but all sons of affected males are unaffected. What is the most likely mode of inheritance?

Accepted Answer

X-linked dominant

Question 7

Which of the following real-world examples is most likely to be influenced by sexually dimorphic traits rather than sex-linked genes?

Accepted Answer

Male pattern baldness

Question 8

In a pedigree, an affected grandfather passes a trait to his grandsons through his daughters, who are not affected. Which inheritance pattern does this suggest?

Accepted Answer

X-linked recessive

Question 9

A woman who is a carrier for an X-linked recessive disorder has children with a man who is affected by the disorder. What is the probability that their daughter will be affected?

Accepted Answer

$$\frac{1}{4}$$

Question 10

Which statement about Y-linked inheritance is correct?

Accepted Answer

All male descendants of an affected man will exhibit the trait.

Question 11

A pedigree shows a trait that appears only in males and is present in every generation. Which of the following is the most likely explanation?

Accepted Answer

Y-linked inheritance

Question 12

If a carrier female for an X-linked recessive trait ($$X^AX^a) $$mates with an affected male ($$X^aY$$), what is the probability that their son will be affected?

Accepted Answer

$$\frac{1}{2}$$

Question 13

Which of the following is a distinguishing feature of X-linked dominant inheritance compared to autosomal dominant inheritance?

Accepted Answer

Affected males transmit the trait to all daughters but not to sons.

Question 14

A pedigree shows that a trait is present in both males and females, but only males pass the trait to their sons. Which inheritance pattern does this suggest?

Accepted Answer

Y-linked

Question 15

Which equation correctly represents the probability that a carrier female ($$X^AX^a) $$and a normal male ($$X^AY) $$will have a daughter who is a carrier for an X-linked recessive trait?

Accepted Answer

$$\frac{1}{2}$$

Question 16

Which of the following is a real-world example of an X-linked dominant disorder?

Accepted Answer

Hypophosphatemia

Question 17

A pedigree shows that a trait is present in every generation, but only females are affected. Which inheritance pattern is most likely?

Accepted Answer

X-linked dominant

Question 18

Which of the following statements about X-linked recessive inheritance is FALSE?

Accepted Answer

Trait is equally common in males and females.

Question 19

A pedigree shows a trait that skips generations and appears in both males and females. Which inheritance pattern is most likely?

Accepted Answer

Autosomal recessive

Question 20

Which of the following best describes the inheritance pattern of the hairy ears trait in humans?

Accepted Answer

It is a complex phenotype possibly involving autosomal genes and/or effects of testosterone.

Sex-Linked and Sexually Dimorphic Traits: Patterns of Inheritance in Humans

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