Question 1

Which of the following best describes the role of epigenetic markers in chromatin remodeling?

Accepted Answer

Epigenetic markers can promote both open chromatin (gene activation) and chromatin compaction (gene silencing).

Question 2

Which of the following is a key property of constitutive heterochromatin?

Accepted Answer

It only unpacks for replication and remains condensed otherwise.

Question 3

A gene is relocated near a centromere due to chromosomal rearrangement and shows patchy expression in the organism. What is the most likely explanation for this phenomenon?

Accepted Answer

The gene is subject to positional effect variegation (PEV), where heterochromatin spreads and silences the gene in some cells.

Question 4

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

Accepted Answer

Alternative splicing

Question 5

Which of the following best explains how insulators function in the genome?

Accepted Answer

They block the spreading of heterochromatin and can prevent enhancers from activating promoters when placed between them.

Question 6

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

Accepted Answer

HP1 (Heterochromatin Protein 1)

Question 7

Which of the following is TRUE regarding facultative heterochromatin?

Accepted Answer

It retains the potential to convert back to euchromatin and contains genes that are currently silenced.

Question 8

Which of the following best describes the difference between constitutive and facultative heterochromatin?

Accepted Answer

Facultative heterochromatin can become euchromatin, while constitutive heterochromatin remains condensed except for replication.

Question 9

Which of the following is a direct molecular consequence of genomic imprinting?

Accepted Answer

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

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 of the following statements about X chromosome inactivation in mammals is CORRECT?

Accepted Answer

X inactivation is random and occurs early in embryogenesis, resulting in mosaicism in females.

Question 12

Which region is necessary and sufficient for X chromosome inactivation in mammals?

Accepted Answer

X inactivation center (Xic)

Question 13

Which of the following best describes the role of Polycomb Repressive Complexes (PRCs) in facultative heterochromatin?

Accepted Answer

PRCs are required for the maintenance (memory) of the inactive state, not for initial repression.

Question 14

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

Accepted Answer

Doubling the expression of the single X chromosome in males

Question 15

Which of the following is a key difference between X inactivation and genomic imprinting?

Accepted Answer

X inactivation is random and occurs early in embryogenesis, while imprinting is parent-specific and established in gametes.

Question 16

Which of the following equations best represents the effect of dosage compensation in Drosophila males?

Accepted Answer

$$1X 	imes 2 = 2X$$

Question 17

A female mammal heterozygous for an X-linked loss-of-function allele may show a mosaic phenotype because:

Accepted Answer

X inactivation is random, so some cells express the wild-type allele and others the mutant allele.

Question 18

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

Accepted Answer

Both involve nucleation and spreading mechanisms.

Question 19

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

Accepted Answer

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

Question 20

Which of the following is a real-world consequence of deletions in imprinted gene clusters?

Accepted Answer

They can lead to diseases such as Angelman syndrome, with symptoms depending on which genes are affected.

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

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