Question 1

Which of the following best describes the difference between the XX/XY and ZZ/ZW systems of sex determination?

Accepted Answer

In the XX/XY system, females are homogametic and males are heterogametic, while in the ZZ/ZW system, males are homogametic and females are heterogametic.

Question 2

A human individual with the karyotype 47,XXY is most likely to exhibit which syndrome, and what is a common phenotypic characteristic?

Accepted Answer

Klinefelter syndrome; tall stature and reduced body hair

Question 3

Which region of the human Y chromosome is responsible for initiating male development, and what protein does it encode?

Accepted Answer

SRY; Testis-determining factor (TDF)

Question 4

A phenotypically female patient is found to have a Y chromosome with a deletion. Which region is most likely deleted to explain her phenotype?

Accepted Answer

SRY region

Question 5

In mammals, dosage compensation is achieved by which of the following mechanisms?

Accepted Answer

Inactivating one X chromosome in females

Question 6

According to the N-1 rule, how many Barr bodies would you expect in a cell with a 48,XXXX karyotype?

Accepted Answer

$$N-1 = 4-1 = 3$$

Question 7

A calico cat is cloned from a cell in which the X chromosome carrying the orange allele is inactive. What will be the coat color of the cloned cat?

Accepted Answer

The cloned cat will have only black and white fur.

Question 8

Which of the following statements best describes the Lyon hypothesis?

Accepted Answer

One of the two female X chromosomes is randomly inactivated in an early embryonic stage.

Question 9

In Drosophila, what determines the sex of an individual?

Accepted Answer

The ratio of X chromosomes to sets of autosomes

Question 10

A Drosophila fly has three X chromosomes and two sets of autosomes (3X:2A). What is its sexual phenotype?

Accepted Answer

Metafemale

Question 11

Which of the following is a real-world example of temperature-dependent sex determination?

Accepted Answer

Sex determination in crocodiles

Question 12

A man observes a Barr body in his epithelial cells. What is the most likely karyotype?

Accepted Answer

47,XXY

Question 13

Which gene is responsible for X chromosome inactivation in mammals, and what does it produce?

Accepted Answer

Xist; a non-coding RNA

Question 14

In C. elegans, which karyotype results in a hermaphrodite?

Accepted Answer

XX

Question 15

Which of the following best explains why X-inactivation does not completely prevent symptoms in Turner or Klinefelter syndromes?

Accepted Answer

Delayed inactivation and escape of some genes from inactivation.

Question 16

A mutation inactivates Xist on one X chromosome in a female. What is the predicted outcome?

Accepted Answer

The mutant chromosome would always be active.

Question 17

Which of the following is an example of epigenetics as discussed in the context of sex chromosomes?

Accepted Answer

X chromosome inactivation

Question 18

If nondisjunction occurs during meiosis I in a human male, which of the following karyotypes could result in the offspring?

Accepted Answer

45,X

Question 19

Which of the following best describes the secondary sex ratio in humans?

Accepted Answer

It is typically greater than 1, with more males born than females.

Sex Determination and Sex Chromosomes: Mechanisms, Syndromes, and Dosage Compensation

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