Question 1

Which of the following best describes the role of epigenetic markers in chromatin structure and gene expression?

Accepted Answer

Epigenetic markers determine chromatin state, which can either promote open chromatin (gene activation) or compaction (gene silencing).

Question 2

A gene normally located in euchromatin is moved near heterochromatin due to a chromosomal rearrangement. What is the most likely outcome for this gene's expression, and what is this phenomenon called?

Accepted Answer

The gene will show patchy expression due to stochastic spreading of heterochromatin; this is called positional effect variegation (PEV).

Question 3

Which of the following is a key difference between constitutive and facultative heterochromatin?

Accepted Answer

Facultative heterochromatin contains genes that are currently silenced but can become active, while constitutive heterochromatin remains condensed and gene-poor.

Question 4

Which molecular mechanism is NOT directly involved in the formation of heterochromatin?

Accepted Answer

RNA splicing

Question 5

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

Accepted Answer

Inactivation of one X chromosome in females, forming a Barr body

Question 6

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

Accepted Answer

X inactivation is random in embryonic cells and is perpetuated in all daughter cells.

Question 7

What is the function of the X inactivation center (Xic) on the X chromosome?

Accepted Answer

It is a cis-element necessary and sufficient to induce X inactivation, expressing long noncoding RNAs such as Xist.

Question 8

Which of the following best explains why female mammals are considered mosaics for X-linked gene expression?

Accepted Answer

Each cell randomly inactivates either the maternal or paternal X chromosome, leading to patches of cells expressing different alleles.

Question 9

Which of the following is a defining feature of genomic imprinting?

Accepted Answer

Only one allele is expressed, and which allele is active depends on the parent of origin.

Question 10

A deletion in the imprinted gene cluster on chromosome 15q11–q13 can lead to which of the following syndromes?

Accepted Answer

Angelman syndrome

Question 11

Which protein is essential for the formation and spreading of constitutive heterochromatin in mammals?

Accepted Answer

HP1 (Heterochromatin Protein 1)

Question 12

Which of the following statements about Polycomb (PcG) and Trithorax (TrxG) group proteins is correct?

Accepted Answer

PcG proteins maintain gene repression, while TrxG proteins maintain gene activation at the same DNA element.

Question 13

Which of the following mechanisms can block the spreading of heterochromatin and prevent positional effect variegation (PEV)?

Accepted Answer

Insulators flanking a gene

Question 14

Which of the following is TRUE regarding the inheritance of epigenetic changes?

Accepted Answer

Epigenetic changes can be inherited and lead to mutant phenotypes without altering the DNA sequence.

Question 15

Which of the following best describes the molecular basis of genomic imprinting?

Accepted Answer

Allele-specific DNA methylation leads to inactivation of one allele.

Question 16

Which of the following is an example of facultative heterochromatin?

Accepted Answer

Inactivated X chromosome

Question 17

Which of the following best explains why only a small percentage of human genes are subject to genomic imprinting?

Accepted Answer

Imprinted genes tend to cluster in specific chromosomal regions, and only certain genes have the necessary cis-elements for imprinting.

Question 18

A female who is heterozygous for an X-linked loss-of-function mutation may show a phenotype if:

Accepted Answer

The normal allele is inactivated in a majority of cells in a tissue where the gene is critical.

Question 19

Which of the following is a similarity between constitutive and facultative heterochromatin?

Accepted Answer

Both involve nucleation at specific points and spreading to neighboring regions.

Question 20

Which of the following is a correct statement about the maintenance of repression in facultative heterochromatin?

Accepted Answer

PRCs are required for the maintenance (memory) of inactive states, but initial repression is established by sequence-specific repressors.

Epigenetics: Chromatin States, Heterochromatin, Dosage Compensation, and Genomic Imprinting

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