Question 1

Which of the following best explains why X-linked recessive disorders, such as color blindness, are more common in males than females?

Accepted Answer

Males are hemizygous for the X chromosome, so a single recessive allele will determine the phenotype.

Question 2

In Morgan’s classic experiment with Drosophila, a white-eyed male was crossed with a wild-type female. All F1 offspring had red eyes. When F1 were crossed, the F2 generation showed all females with red eyes and half the males with white eyes. Which inheritance pattern does this illustrate?

Accepted Answer

Crisscross inheritance pattern of X-linked recessive alleles

Question 3

A male fruit fly with genotype $$X^wY ($$where $$w is a $$recessive allele for white eyes) is crossed with a female with genotype $$X^+X^w. $$What proportion of their male offspring will have white eyes?

Accepted Answer

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

Question 4

Which term describes the phenomenon where a single recessive allele determines the phenotype in males for X-linked traits?

Accepted Answer

Pseudodominance

Question 5

Why do males never pass X-linked recessive traits to their sons?

Accepted Answer

Because males only donate a Y chromosome to their sons.

Question 6

Which of the following best describes dosage compensation in mammals?

Accepted Answer

Decreasing expression of X-linked genes in females by inactivating one X chromosome

Question 7

What is the Barr body?

Accepted Answer

A condensed, transcriptionally inactive X chromosome in female cells

Question 8

Which gene on the Y chromosome is responsible for male sex determination in humans?

Accepted Answer

SRY (Sex-determining region Y)

Question 9

A calico cat displays patches of different colors due to random X chromosome inactivation. What genetic principle does this illustrate?

Accepted Answer

Mosaicism

Question 10

Which of the following is true about sex-limited traits?

Accepted Answer

They are expressed only in one gender, but the genes are autosomal and present in both sexes.

Question 11

In the context of nondisjunction, what is the expected outcome if a gamete with two copies of chromosome 21 is fertilized by a normal gamete?

Accepted Answer

Trisomy 21 (Down syndrome)

Question 12

Based on the graph showing the incidence of Down syndrome with maternal age, which statement is most accurate?

Accepted Answer

The risk of Down syndrome increases with maternal age.

Question 13

Which region of the Y chromosome allows pairing with the X chromosome during meiosis?

Accepted Answer

Pseudoautosomal region

Question 14

In reptiles such as the American alligator, what environmental factor can influence sex determination?

Accepted Answer

Temperature during embryonic development

Question 15

If a female is heterozygous for an X-linked recessive trait, what proportion of her sons will express the trait, assuming the father is unaffected?

Accepted Answer

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

Question 16

Which of the following best describes sex-influenced traits?

Accepted Answer

Phenotype is seen in both genders, but one gender shows dominant phenotype while the other shows recessive.

Question 17

Which mechanism is used for dosage compensation in Drosophila?

Accepted Answer

Increase expression of X-linked genes in males

Question 18

A female fruit fly with genotype $$X^wX^w ($$white-eyed) is crossed with a male with genotype $$X^+Y ($$red-eyed). What proportion of their female offspring will have white eyes?

Accepted Answer

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

Question 19

Which of the following statements about X chromosome inactivation is correct?

Accepted Answer

Inactivation is random in mammals, and all descendants of a cell will have the same X chromosome inactivated.

Question 20

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

Accepted Answer

Males can pass X-linked traits to their sons.

Sex Linkage, Sex Chromosomes, and Dosage Compensation in Genetics

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