Question 1

Which of the following statements correctly describes the synthesis of the leading and lagging strands during DNA replication at the replication fork?

Accepted Answer

The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously away from the fork in the form of Okazaki fragments.

Question 2

In a genetic cross involving two genes on the same chromosome, which of the following would most likely result in a deviation from Mendel's expected 9:3:3:1 ratio in the F2 generation?

Accepted Answer

The genes are located close together on the same chromosome and exhibit genetic linkage.

Question 3

Which of the following best explains why recombination frequency ($RF$) between two genes is not always proportional to their physical distance in base pairs?

Accepted Answer

Recombination frequency is influenced by chromosomal features such as hotspots and coldspots, which can increase or decrease crossover rates independent of physical distance.

Question 4

A double heterozygote for two linked genes is crossed with a tester (homozygous recessive for both genes). If the observed recombinant frequency is 13.2% for gene pair B-C and 6.4% for A-B, what is the expected recombinant frequency for A-C?

Accepted Answer

$RF(A-C) = 18.5\%$

Question 5

Which enzyme is responsible for actively producing double-strand breaks (DSBs) during homologous recombination in meiosis?

Accepted Answer

Spo11

Question 6

During the Double-Strand Break Repair (DSBR) model of homologous recombination, what is the role of the 3' overhang created by exonuclease activity?

Accepted Answer

It invades the homologous duplex DNA to initiate strand exchange and form a D-loop.

Question 7

Which of the following outcomes is possible when resolving the two Holliday junctions formed during DSBR?

Accepted Answer

Both crossover and non-crossover (patch) products can be formed, depending on the orientation of the cuts.

Question 8

A mutation abolishes the formation of the synaptonemal complex during meiosis. What is the most likely consequence for homologous recombination?

Accepted Answer

Recombinant chromosomes will still be generated, indicating that the synaptonemal complex is not required for recombination.

Question 9

Which repair pathway is most likely to result in gene conversion without crossover during mitosis?

Accepted Answer

Synthesis-Dependent Strand Annealing (SDSA)

Question 10

Which of the following diseases can arise from the loss of DNA sequences between direct repeats due to the Single-Strand Annealing (SSA) mechanism?

Accepted Answer

Type 1 diabetes, Fabry disease, and hemophilia

Question 11

Which of the following statements about the synaptonemal complex is correct?

Accepted Answer

It is required for the pairing and synapsis of homologous chromosomes during meiosis.

Question 12

In the context of homologous recombination, what is a D-loop?

Accepted Answer

A region where the invading 3' single-stranded DNA displaces a strand in the homologous duplex, forming a loop structure.

Question 13

Which of the following mechanisms is most likely to result in chromosome rearrangements due to imprecise repair?

Accepted Answer

Non-homologous end joining (NHEJ)

Question 14

During meiosis, homologous chromosomes pair and undergo recombination. Which phase of meiosis is this most likely to occur?

Accepted Answer

Prophase I

Question 15

Which of the following is a key difference between crossover and non-crossover (patch) recombination products?

Accepted Answer

Crossover products result in the exchange of flanking genetic markers between homologous chromosomes, while non-crossover products do not.

Question 16

If a double-strand break occurs between two direct repeats on a chromosome, which repair mechanism is most likely to result in the loss of the intervening DNA sequence?

Accepted Answer

Single-strand annealing (SSA)

Question 17

Which of the following best describes gene conversion?

Accepted Answer

A process where one allele is replaced by another due to mismatch repair following homologous recombination.

Question 18

Which of the following is true regarding the relationship between genetic linkage and independent assortment?

Accepted Answer

Genes that are far apart on the same chromosome may assort independently due to frequent crossovers.

Question 19

Which of the following is a consequence of homologous recombination during meiosis?

Accepted Answer

It increases genetic diversity by shuffling alleles between homologous chromosomes.

Question 20

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

Okazaki fragments are short DNA segments synthesized on the lagging strand during DNA replication.

DNA Recombination and Linkage Mapping in Genetics

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