Question 1

Which of the following best describes a frameshift mutation and its likely effect on a protein?

Accepted Answer

An insertion or deletion of bases not in multiples of three, altering the reading frame and usually producing a nonfunctional protein.

Question 2

A patient is exposed to a chemical that adds alkyl groups to guanine bases in DNA. What is the most likely consequence of this exposure at the molecular level?

Accepted Answer

Guanine will mispair with thymine during replication, potentially causing base substitutions.

Question 3

Which DNA repair mechanism is primarily responsible for correcting thymine dimers caused by UV radiation?

Accepted Answer

Nucleotide Excision Repair (NER)

Question 4

A mutation in a gene results in a protein that is completely nonfunctional. What is the most accurate term for this type of mutation?

Accepted Answer

Null mutation

Question 5

Which of the following best explains why most loss-of-function mutations are recessive in diploid organisms?

Accepted Answer

One wild-type allele usually produces enough gene product for a normal phenotype.

Question 6

A researcher finds a DNA sequence with a single base change that does not alter the amino acid sequence of the encoded protein. What type of mutation is this?

Accepted Answer

Silent mutation

Question 7

Which of the following is a potential consequence of chronic exposure to intercalating agents such as ethidium bromide?

Accepted Answer

Increased risk of frameshift mutations due to insertions or deletions during DNA replication.

Question 8

Which of the following best describes the difference between germ line and somatic mutations?

Accepted Answer

Germ line mutations are heritable and contribute to evolution, while somatic mutations affect only the individual.

Question 9

A DNA repair enzyme removes a uracil base from DNA and replaces it with cytosine. Which repair pathway is responsible for this correction?

Accepted Answer

Base Excision Repair (BER)

Question 10

Which of the following is a direct result of ionizing radiation (IR) exposure at the chromosomal level?

Accepted Answer

Chromosome breaks (clastogenic effects)

Question 11

A DNA sequence originally reads 5'-ATG GAA TGC-3'. After a mutation, it reads 5'-ATG GAG TGC-3'. What type of mutation has occurred, and what is the likely effect on the protein?

Accepted Answer

Substitution; missense mutation that may change one amino acid

Question 12

Which of the following best describes the process of depurination in DNA?

Accepted Answer

Hydrolysis of the glycosidic bond, resulting in loss of a purine base

Question 13

A patient receives a high dose of X-rays during a medical procedure. Which of the following DNA repair mechanisms is most critical for repairing the resulting double-strand breaks?

Accepted Answer

Double-Strand Break Repair

Question 14

Which of the following is a common endogenous source of DNA mutation?

Accepted Answer

Replication errors during DNA synthesis

Question 15

A DNA polymerase incorporates an incorrect base during replication, but the error is not corrected immediately. Which repair system acts after replication to fix this error?

Accepted Answer

Mismatch Repair

Question 16

Which of the following equations best represents the probability $$P of a $$mutation being passed to the next generation if it occurs in a germ cell, assuming random mating and no selection?

Accepted Answer

$$P = \frac{1}{2}$$

Question 17

A scientist exposes cells to a mutagen that causes the addition of a single base pair. Which of the following is the most likely outcome if this occurs within a coding region?

Accepted Answer

A frameshift mutation that alters the reading frame and likely produces a nonfunctional protein

Question 18

Which of the following best explains why DNA repair systems are essential for cellular health?

Accepted Answer

They correct DNA damage, reducing the risk of cancer and genetic disorders.

Question 19

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

Accepted Answer

Nonsense mutation; results in a truncated protein

Gene Mutation, DNA Repair, and Transposition – Study Notes

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