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 in turn regulates gene accessibility and expression.

Question 2

A gene is normally expressed in all cells, but after a chromosomal rearrangement, it is juxtaposed to heterochromatin and shows patchy expression in the eye of Drosophila. What is this phenomenon called?

Accepted Answer

Positional effect variegation (PEV)

Question 3

Which of the following is a key molecular mechanism involved in the formation of heterochromatin?

Accepted Answer

DNA methylation

Question 4

Which of the following statements about constitutive and facultative heterochromatin is CORRECT?

Accepted Answer

Facultative heterochromatin can convert back to euchromatin and contains genes that are currently silenced.

Question 5

Which protein is essential for the formation and spreading of constitutive heterochromatin in mammals by binding to methylated histone H3K9?

Accepted Answer

HP1 (Heterochromatin Protein 1)

Question 6

What is the primary molecular basis for genomic imprinting?

Accepted Answer

Allele-specific DNA methylation

Question 7

Which of the following is TRUE regarding X chromosome inactivation in mammals?

Accepted Answer

The choice of which X chromosome to inactivate is random and occurs early in embryogenesis.

Question 8

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 9

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 1-2% of genes are regulated this way.

Question 10

Which of the following is a consequence of deleting an imprinted gene cluster on chromosome 15q11–q13 in humans?

Accepted Answer

Development of Angelman syndrome

Question 11

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

Accepted Answer

TrxG proteins maintain active chromatin states, while PcG proteins maintain repressed chromatin states.

Question 12

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

Accepted Answer

Insulators

Question 13

In Drosophila, dosage compensation is achieved by:

Accepted Answer

Doubling the expression of X-linked genes in males

Question 14

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

Accepted Answer

X inactivation is random and long-range, while imprinting is parent-specific and short-range.

Question 15

Which of the following best describes the process of heterochromatin spreading?

Accepted Answer

It can be stochastic, with the extent of spreading differing between progeny cells.

Question 16

Which of the following is TRUE regarding the X inactivation center (Xic)?

Accepted Answer

It is a cis-element that expresses several long noncoding RNAs essential for X inactivation.

Question 17

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

Accepted Answer

Both involve nucleation and spreading mechanisms and use epigenetic markers.

Question 18

A transgene is inserted near heterochromatin and is not expressed in some cells. Which strategy would most likely ensure its expression in all cells?

Accepted Answer

Flanking the transgene with insulator sequences

Question 19

Which of the following histone modifications is most closely associated with constitutive heterochromatin?

Accepted Answer

$$\mathrm{H3K9me3}$$

Question 20

Which of the following best explains why epigenetic changes can lead to mutant phenotypes without altering DNA sequence?

Accepted Answer

Epigenetic changes modify gene expression through chromatin state, not DNA sequence.

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

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