Question 1

Which of the following best explains why humans can produce millions of different antibodies despite having only a few hundred immunoglobulin genes?

Accepted Answer

Somatic recombination and junctional diversity generate a vast array of antibody specificities from a limited set of gene segments.

Question 2

During meiotic recombination, what is the primary molecular event that initiates crossing-over between homologous chromosomes?

Accepted Answer

Double-strand DNA breaks followed by strand invasion

Question 3

A B cell undergoes a V19-J4 recombination in its kappa light chain gene. Can this same B cell later produce a kappa chain with a V5-J2 combination?

Accepted Answer

No, because the intervening DNA is deleted during the initial recombination event.

Question 4

Which of the following is NOT a function of antibodies in the immune response?

Accepted Answer

Direct digestion of antigens

Question 5

Given the following gene segment numbers: 40 V and 5 J segments for kappa light chains, how many possible VJ combinations can be generated for the kappa chain?

Accepted Answer

$$40 	imes 5 = 200$$

Question 6

Which process is responsible for the generation of the five different classes (isotypes) of antibodies that can all recognize the same antigen?

Accepted Answer

Alternative splicing and class-switch recombination at the constant region genes of the heavy chain

Question 7

Which of the following best describes the role of the variable (V) region in an antibody molecule?

Accepted Answer

It is responsible for antigen binding specificity.

Question 8

In the context of antibody gene rearrangement, what is the function of the Recombination Signal Sequences (RSS)?

Accepted Answer

They serve as recognition sites for RAG1 and RAG2 proteins to mediate recombination.

Question 9

Which immunoglobulin class is the first to be secreted during a primary immune response and does not cross the placenta?

Accepted Answer

IgM

Question 10

A patient is found to have a deficiency in RAG1 and RAG2 proteins. Which aspect of their immune system would be most directly affected?

Accepted Answer

Somatic recombination of antibody genes in B cells

Question 11

Which of the following statements about the clonal selection theory is correct?

Accepted Answer

Only B cells with receptors specific to an encountered antigen proliferate and differentiate into plasma cells.

Question 12

How does class-switch recombination (CSR) alter the antibody produced by a B cell?

Accepted Answer

It changes the constant region of the heavy chain, altering the antibody's effector function but not its antigen specificity.

Question 13

Which of the following best describes the process of opsonization?

Accepted Answer

Antibodies bind to antigens, marking them for phagocytosis by immune cells such as macrophages.

Question 14

If a B cell has already undergone a V-D-J recombination in its heavy chain gene, what is the next step required to produce a functional heavy chain protein?

Accepted Answer

Alternative splicing to join the VDJ region to a constant (C) region gene

Question 15

Which of the following is a direct consequence of the random nature of V(D)J recombination in B cells?

Accepted Answer

Each B cell produces a unique antibody specificity.

Question 16

Which of the following best explains why IgG, IgA, and IgE antibodies produced by the same B cell can all recognize the same antigen?

Accepted Answer

They share the same recombined VDJ region, which determines antigen specificity.

Question 17

A mutation in the switch (S) sequences of the heavy chain constant region genes would most likely impair which process?

Accepted Answer

Class-switch recombination (CSR) to produce different antibody isotypes

Question 18

Which of the following best describes the role of memory B cells in the immune response?

Accepted Answer

They persist long-term and enable a faster and stronger response upon re-exposure to the same antigen.

Question 19

Calculate the number of possible VDJ combinations for the heavy chain, given 51 V, 27 D, and 6 J gene segments.

Accepted Answer

$$51 	imes 27 	imes 6 = 8262$$

Question 20

Which of the following statements about the structure of an antibody is correct?

Accepted Answer

Each antibody consists of two identical heavy chains and two identical light chains, forming a Y-shaped tetramer.

Genetic Recombination and Antibody Diversity in Eukaryotic Genomes

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