Question 1

Which experimental result would best support the random mutation hypothesis as tested by Luria and Delbrück in their fluctuation test?

Accepted Answer

Different bacterial cultures show large variations in the number of phage-resistant colonies due to mutations occurring at random times.

Question 2

A mutation changes a codon from UAU (tyrosine) to UAC (tyrosine). What type of mutation is this, and what is its likely effect on the protein?

Accepted Answer

Synonymous mutation; no change in the amino acid sequence.

Question 3

Which of the following best describes a frameshift mutation?

Accepted Answer

One or more base pairs are inserted or deleted, altering the reading frame and potentially producing a nonfunctional protein.

Question 4

A mutation in the -35 region of a bacterial promoter most likely results in which of the following?

Accepted Answer

Reduced or abolished transcription of the gene.

Question 5

A mutation at the 5' splice site of an intron leads to which of the following outcomes?

Accepted Answer

Retention of the intron in the mature mRNA, possibly producing a nonfunctional protein.

Question 6

A base-pair substitution at position 110 of human β-globin intron 1 creates a new AG sequence. What is the most likely consequence?

Accepted Answer

Creation of a cryptic splice site, leading to inclusion of extra nucleotides in the mature mRNA.

Question 7

Which of the following best describes a true reversion mutation?

Accepted Answer

A second mutation restores the original wild-type DNA sequence within the same codon.

Question 8

Which of the following is an example of a second-site reversion (suppressor mutation)?

Accepted Answer

A mutation in gene A is compensated by a mutation in gene B, restoring the wild-type phenotype.

Question 9

Strand slippage during DNA replication is most likely to cause which type of mutation?

Accepted Answer

Frameshift mutation due to insertion or deletion of repeat units

Question 10

Which of the following diseases is associated with trinucleotide repeat expansion?

Accepted Answer

Huntington disease

Question 11

Depurination of DNA results in which of the following?

Accepted Answer

Loss of a purine base, creating an apurinic site

Question 12

Which chemical mutagen acts as a nucleotide base analog and can cause transition mutations by pairing with both adenine and guanine?

Accepted Answer

5-bromodeoxyuridine

Question 13

Which type of DNA damage is most commonly caused by UV irradiation?

Accepted Answer

Thymine dimers (photoproducts)

Question 14

The Ames test is used to determine whether a chemical compound is mutagenic. Which result would indicate that a compound is mutagenic?

Accepted Answer

A significant increase in the number of his+ revertant colonies compared to the control.

Question 15

Which DNA repair mechanism is responsible for removing and replacing a single damaged base, such as uracil in DNA?

Accepted Answer

Base excision repair (BER)

Question 16

In E. coli, how does the mismatch repair system distinguish the newly synthesized DNA strand from the template strand?

Accepted Answer

By the presence of methylation on the template strand.

Question 17

Which protein is directly responsible for activating the p53 repair pathway in response to DNA damage in humans?

Accepted Answer

ATM

Question 18

Which DNA repair mechanism is error-prone and allows replication to proceed across damaged DNA in E. coli?

Accepted Answer

Translesion DNA synthesis (SOS repair)

Question 19

Which of the following best describes nonhomologous end joining (NHEJ)?

Accepted Answer

An error-prone repair mechanism that ligates broken DNA ends together, often resulting in loss of nucleotides.

Question 20

Which enzyme is responsible for generating the programmed double-strand breaks that initiate homologous recombination during meiosis in eukaryotes?

Accepted Answer

Spo11

Gene Mutation, DNA Repair, and Homologous Recombination: Study Notes for Genetics Students

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