Question 1

Which statement best describes dosage compensation in human females?

Accepted Answer

One X chromosome is randomly inactivated in each cell, so females express X-linked genes at levels similar to males.

Question 2

According to the Lyon hypothesis, what is the expected number of Barr bodies in a cell from a female with karyotype 47,XXX?

Accepted Answer

$$2$$

Question 3

Which of the following is TRUE regarding the XIST gene and its role in X chromosome inactivation?

Accepted Answer

XIST produces an IncRNA that coats and inactivates the X chromosome.

Question 4

A female is heterozygous for a gene on the X chromosome. According to dosage compensation, what is observed in her cells?

Accepted Answer

Only one allele is expressed in each cell, but different cells may express different alleles.

Question 5

Which of the following karyotypes would NOT have any Barr bodies present in their cells?

Accepted Answer

46,XY

Question 6

If a woman has the karyotype 48,XXXX, how many Barr bodies would you expect to find in her somatic cells?

Accepted Answer

$$3$$

Question 7

Which process ensures that males and females have similar levels of X-linked gene expression?

Accepted Answer

Random inactivation of one X chromosome in females

Question 8

Which of the following is a cytological marker for X chromosome inactivation?

Accepted Answer

Barr body

Question 9

A male with Klinefelter syndrome (47,XXY) will have how many Barr bodies per somatic cell?

Accepted Answer

$$1$$

Question 10

Which of the following best explains why females are considered genetic mosaics for X-linked traits?

Accepted Answer

Each cell randomly inactivates one X chromosome, leading to different populations of cells expressing different alleles.

Question 11

Which of the following is NOT a feature of the Y chromosome compared to the X chromosome?

Accepted Answer

Contains more genes than the X chromosome

Question 12

If a female is heterozygous for the G6PD gene on the X chromosome, what would you expect to observe in a biochemical assay of her hair follicles?

Accepted Answer

Some follicles express only one isozyme, while others express the other isozyme.

Question 13

Which of the following statements about Barr bodies is correct?

Accepted Answer

Barr bodies are composed of inactive X chromosomal material.

Question 14

What is the primary function of XIST IncRNA in X chromosome inactivation?

Accepted Answer

It coats the inactive X chromosome and modifies histones to maintain silencing.

Question 15

Which of the following is a direct consequence of random X chromosome inactivation in females?

Accepted Answer

Females are mosaics for X-linked gene expression.

Question 16

A female with Turner syndrome (45,X) will have how many Barr bodies per somatic cell?

Accepted Answer

$$0$$

Question 17

Which of the following best describes the maintenance phase of X chromosome inactivation?

Accepted Answer

The inactive X chromosome remains silenced through subsequent cell divisions.

Question 18

Which of the following is NOT evidence for dosage compensation?

Accepted Answer

Transcription of both X chromosomes in every female cell

Question 19

Which of the following is a key prediction of the Lyon hypothesis?

Accepted Answer

Females with more than two X chromosomes will have one less Barr body than the number of X chromosomes.

Question 20

Which of the following best explains why X-linked recessive diseases are more common in males than females?

Accepted Answer

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

X- and Y-Linked Inheritance, Dosage Compensation, and the Lyon Hypothesis

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