Q: Which equation correctly represents the probability of a son being color blind if his mother is a carrier (X^B X^b) and his father has normal vision (X^B Y)?

$$P(\text{color blind son}) = \frac{1}{2}$$

Q: A male with hemophilia (an X-linked recessive disorder) marries a woman who is not a carrier. What is the probability that their daughters will be carriers?

$$P(\text{carrier daughter}) = 1$$

Question 1

Which of the following best describes the role of the SRY gene in human sex determination?

Accepted Answer

SRY gene influences the undifferentiated gonad to form testis, which produces testosterone and anti-Mullerian hormone.

Question 2

In the XO sex determination system, which of the following is true?

Accepted Answer

Males have one X chromosome and females have two X chromosomes.

Question 3

A female cat is heterozygous for the X-linked coat color gene (one allele for black fur, one for orange fur). What is the genetic basis for the calico (tortoiseshell) pattern observed in her coat?

Accepted Answer

Random X-inactivation in somatic cells leads to patches where either the black or orange allele is expressed.

Question 4

Which equation correctly represents the probability of a son being color blind if his mother is a carrier (X^B X^b) and his father has normal vision (X^B Y)?

Accepted Answer

$$P(	ext{color blind son}) = \frac{1}{2}$$

Question 5

Which of the following statements about dosage compensation in mammals is correct?

Accepted Answer

Dosage compensation equalizes the amount of protein produced by X-linked genes in males and females by inactivating one X chromosome in females.

Question 6

A male with hemophilia (an X-linked recessive disorder) marries a woman who is not a carrier. What is the probability that their daughters will be carriers?

Accepted Answer

$$P(	ext{carrier daughter}) = 1$$

Question 7

Which of the following is a consequence of the Lyon hypothesis regarding X-inactivation?

Accepted Answer

Once X-inactivation occurs in a cell, all its progeny cells have the same X chromosome inactivated.

Question 8

In birds, which sex is heterogametic and what is their chromosomal composition?

Accepted Answer

Females are heterogametic (ZW).

Question 9

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 result in the disorder.

Question 10

In the haplodiploidy sex determination system found in bees, what is the chromosomal composition of males and females?

Accepted Answer

Males are haploid (from unfertilized eggs) and females are diploid (from fertilized eggs).

Question 11

A woman is a carrier for color blindness (X^B X^b) and her husband is color blind (X^b Y). What is the probability that their daughter will be color blind?

Accepted Answer

$$P(	ext{color blind daughter}) = \frac{1}{2}$$

Question 12

Which scientist is credited with discovering sex-linked inheritance through experiments with Drosophila melanogaster?

Accepted Answer

Thomas Hunt Morgan

Question 13

What is the expected genotype of a female who does not express a sex-linked recessive trait but is a carrier?

Accepted Answer

$$X^A X^a$$

Question 14

Which of the following is true about Barr bodies?

Accepted Answer

Barr bodies are condensed, inactivated X chromosomes found in female somatic cells.

Question 15

A male fly with white eyes (X^w Y) is crossed with a female fly with red eyes (X^W X^w). What proportion of the male offspring will have white eyes?

Accepted Answer

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

Question 16

Which of the following mechanisms is responsible for equalizing the expression of X-linked genes between males and females in mammals?

Accepted Answer

X-inactivation

Question 17

In a population, the frequency of the X-linked recessive allele for color blindness is $$q = 0.1. $$What is the expected frequency of color blind males?

Accepted Answer

$$q = 0.1$$

Question 18

Which of the following is NOT a chromosomal sex determination system?

Accepted Answer

ABO system

Question 19

A female with triple X syndrome (XXX) will have how many Barr bodies in her somatic cells?

Accepted Answer

2

Sex Linkage and Determination: Mechanisms, Inheritance, and Dosage Compensation

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