Question 1

Which of the following best describes the main function of histone proteins in eukaryotic chromatin?

Accepted Answer

They are basic proteins that tightly bind DNA, facilitating chromosome condensation and organization.

Question 2

A researcher observes that a gene, when relocated near heterochromatin, is silenced in some cells but not others, resulting in a mosaic phenotype. What is the most likely explanation for this observation?

Accepted Answer

The gene's position near heterochromatin causes position effect variegation (PEV), leading to variable silencing depending on chromatin spread.

Question 3

Which of the following is a key feature of epigenetic modification?

Accepted Answer

It can be reversible and does not change the DNA sequence, but can be inherited through cell division.

Question 4

In mammals, what is the primary mechanism of dosage compensation for X-linked genes?

Accepted Answer

Random inactivation of one X chromosome in females, forming a Barr body.

Question 5

Which equation correctly represents the relationship between the number of nucleosomes ($n$), the total length of DNA ($L$ in base pairs), and the length of DNA wrapped around each nucleosome ($l$ in base pairs)?

Accepted Answer

$n = \frac{L}{l}$

Question 6

A female cat is heterozygous for the orange fur gene (O/o) located on the X chromosome. What is the most likely explanation for the calico (mosaic) fur pattern observed in such cats?

Accepted Answer

Random inactivation of one X chromosome in each cell leads to patches expressing either the O or o allele.

Question 7

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

Accepted Answer

Constitutive heterochromatin is always condensed and contains repetitive sequences, while facultative heterochromatin can vary in condensation and gene expression.

Question 8

Which modification of histone proteins is most closely associated with increased accessibility of DNA for transcription?

Accepted Answer

Acetylation of histone tails

Question 9

A bacterial cell contains a circular chromosome and several plasmids. Which statement best describes the role of plasmids?

Accepted Answer

Plasmids carry nonessential genes and can be engineered to carry foreign DNA.

Question 10

Which of the following statements about nucleosomes is correct?

Accepted Answer

A nucleosome consists of an octamer of histones (H2A, H2B, H3, H4) with about 146 base pairs of DNA wrapped around it.

Question 11

Which of the following best explains why histone proteins are rich in positively charged amino acids?

Accepted Answer

To facilitate tight binding to the negatively charged DNA backbone.

Question 12

In Drosophila, how is dosage compensation achieved for X-linked genes in males?

Accepted Answer

By upregulating transcription from the single male X chromosome.

Question 13

Which of the following is NOT a characteristic of epigenetic inheritance?

Accepted Answer

It always results in permanent changes to the DNA sequence.

Question 14

A mutation causes the loss of function of the Xist gene in a female mammal. What is the most likely consequence?

Accepted Answer

Failure to inactivate one X chromosome, leading to overexpression of X-linked genes.

Question 15

Which of the following best describes the role of SMC (structural maintenance of chromosome) proteins in bacteria?

Accepted Answer

They help condense DNA into smaller loops, contributing to chromosome compaction.

Question 16

If a gene is relocated near a region of constitutive heterochromatin, what is the most likely effect on its expression?

Accepted Answer

It will be silenced due to the highly compacted chromatin environment.

Question 17

Which of the following equations represents the total number of base pairs ($B$) in a chromosome if there are $n$ nucleosomes, each with $l$ base pairs wrapped around it, and $d$ base pairs of linker DNA between nucleosomes?

Accepted Answer

$B = n 	imes (l + d)$

Question 18

Which of the following statements about chromatin structure and gene expression is correct?

Accepted Answer

Open (euchromatic) regions are more accessible to transcription factors and are associated with active gene expression.

Question 19

Which of the following is a real-world example of X-chromosome inactivation leading to a mosaic phenotype?

Accepted Answer

A calico cat with patches of orange and black fur.

Chromosome Structure and Organization in Prokaryotes and Eukaryotes

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