Question 1

Which of the following best explains why Morgan’s discovery of the white-eyed trait in Drosophila was significant for chromosome theory of inheritance?

Accepted Answer

It demonstrated that the behavior of chromosomes correlates with the inheritance of specific traits.

Question 2

In mammals, which combination of sex chromosomes results in a male offspring?

Accepted Answer

$$XY$$

Question 3

A color-blind male marries a woman who is a carrier for color blindness. What is the probability that their daughter will be color blind?

Accepted Answer

$$0.25$$

Question 4

Which statement about X-linked recessive traits is correct?

Accepted Answer

Female parents can pass X-linked alleles to both male and female offspring.

Question 5

What is the expected phenotype ratio for sons of a carrier female (heterozygous for an X-linked recessive allele) and a normal male?

Accepted Answer

Half of the sons will be affected.

Question 6

Which process is responsible for the formation of Barr bodies in female mammals?

Accepted Answer

X chromosome inactivation

Question 7

A tortoiseshell cat has patches of orange and black fur. This phenotype is best explained by:

Accepted Answer

Random X chromosome inactivation in each cell

Question 8

If a male with hemophilia (an X-linked recessive disorder) marries a woman who is not a carrier, what is the probability that their son will have hemophilia?

Accepted Answer

$$0$$

Question 9

Which of the following best describes the genetic mechanism underlying X chromosome inactivation?

Accepted Answer

RNA products from the X chromosome attach to and inactivate it.

Question 10

In humans, why are X-linked disorders more common in males than in females?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will cause the disorder.

Question 11

Which of the following crosses could produce a color-blind female?

Accepted Answer

Color-blind male × carrier female

Question 12

What is the function of the SRY gene located on the Y chromosome?

Accepted Answer

It determines male sex by initiating testis development.

Question 13

Which of the following is a consequence of X chromosome inactivation in female mammals?

Accepted Answer

All descendants of a cell have the same inactive X chromosome.

Question 14

A female who is heterozygous for an X-linked trait will express the trait in:

Accepted Answer

About half of her cells due to random X inactivation.

Question 15

Which of the following best describes the inheritance pattern of X-linked recessive traits?

Accepted Answer

Affected males inherit the allele from their mothers.

Question 16

If a female is homozygous for a normal allele and a male is affected by an X-linked recessive disorder, what is the probability that their daughter will be a carrier?

Accepted Answer

$$1.00$$

Question 17

Which of the following statements about Barr bodies is correct?

Accepted Answer

A Barr body is an inactivated X chromosome found in female cells.

Question 18

Which of the following is NOT a possible genotype for a human female?

Accepted Answer

$$XY$$

Question 19

Which of the following best explains why X-linked disorders are less common in females?

Accepted Answer

Females have two X chromosomes, so a normal allele can mask the effect of a recessive allele.

Question 20

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

Accepted Answer

Duchenne muscular dystrophy

12.2

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