D1.3 Mutations and gene editing
Practice exam-style IB Biology questions for Mutations and gene editing, aligned with the syllabus and grouped by topic.
Question 1
A coding DNA sequence changes from ATG CCA TTT to ATG CGA TTT. What type of gene mutation has occurred?
A.
Insertion
B.
Frameshift
C.
Deletion
D.
Substitution
Question 2
A base substitution changes the mRNA codon from GAA to GAG. Both codons specify glutamic acid. What is the consequence for the polypeptide?
A.
The amino acid sequence is unchanged.
B.
An extra amino acid is inserted.
C.
All following amino acids are changed.
D.
The polypeptide is shortened at that codon.
Question 3
What is a mutagen?
A.
An agent that increases the rate of mutation
B.
An enzyme that copies DNA without errors
C.
A base sequence that codes for a protein
D.
A cell that gives rise to gametes
Question 4
A mutation occurs in a skin cell of an adult human. What is the usual consequence for inheritance?
A.
It immediately becomes present in every body cell.
B.
It is passed to all offspring through gametes.
C.
It always causes cancer in the tissue.
D.
It is not passed to offspring because the cell is somatic.
Question 5
What is the original source of new alleles in a population?
A.
Random fertilization
B.
Independent assortment
C.
Natural selection
D.
Gene mutation
Question 6
A gene is deliberately made inoperative in a mouse and the mice fail to form normal whiskers. What inference is best supported?
A.
The gene has no function in any cell.
B.
The gene sequence is identical in all mammals.
C.
The mutation must be naturally beneficial.
D.
The normal gene is likely to have a role in whisker development.
Question 7
A short DNA sequence in a gene is shown.
Original: TAC GGA CTT
State the type of mutation if the sequence becomes TAC GCA CTT.
[1]
Distinguish between an insertion and a deletion mutation.
[1]
Question 8
One nucleotide is deleted near the start of a coding sequence. What is the most likely effect on translation?
A.
No codon after the deletion can be affected.
B.
Exactly one amino acid is removed with no other effect.
C.
Only one amino acid is replaced by another amino acid.
D.
A frameshift changes many codons after the deletion.
Question 9
What is meant by mutation being random with respect to an organism’s needs?
A.
Mutations occur only after natural selection acts.
B.
Only harmful mutations occur in coding sequences.
C.
Every base in the genome mutates at the same rate.
D.
Mutations are not directed to produce useful traits.
Question 10
What is a knockout library?
A.
A set of guide RNAs copied from one chromosome
B.
A collection of strains, each with a different inactivated gene
C.
A group of organisms selected for high mutation rate
D.
A database of all possible codons and amino acids
Question 11
What is the role of guide RNA in CRISPR-Cas9 gene editing?
A.
It replaces DNA polymerase during chromosome replication.
B.
It prevents all off-target changes in the genome.
C.
It joins cut DNA ends by forming peptide bonds.
D.
It directs Cas9 to a complementary target DNA sequence.
Question 12
Why are there international efforts to harmonize regulation of genome editing technologies?
A.
All countries already permit identical uses of embryo editing.
B.
Ethical issues occur only in prokaryotic CRISPR systems.
C.
CRISPR-Cas9 cannot be used unless regulations are removed.
D.
Different national rules can lead to inconsistent safety and ethical standards.
Question 13
What chemical interaction allows a guide RNA to recognize its target DNA sequence?
A.
Ionic bonding between adjacent amino acids
B.
Hydrogen bonding between complementary bases
C.
Peptide bonding between RNA nucleotides and DNA nucleotides
D.
Covalent bonding between Cas9 and every base
Question 14
A base substitution changes a codon in a coding sequence.
State what is meant by a single-nucleotide polymorphism (SNP).
[1]
Explain why a base substitution may not change the amino acid sequence of a polypeptide.
[1]
Question 15
A single nucleotide is inserted into the middle of a coding sequence.
State the term for a mutation that changes the grouping of bases into codons.
[1]
Explain why this mutation is likely to make the polypeptide non-functional.
[1]
Question 16
Tobacco smoke and ultraviolet radiation can increase mutation rate.
State one chemical mutagen found in tobacco smoke.
[1]
Outline how mutagens can cause gene mutation.
[1]
Question 17
A mutation occurs in a cell lineage.
Define a germ cell.
[1]
Distinguish between the inheritance consequences of a mutation in a germ cell and a mutation in a somatic cell.
[1]
Question 18
Mutation is important in populations even though most new mutations are neutral or harmful.
State how mutation can create a new allele.
[1]
Explain why mutation is essential for evolution by natural selection over long time scales.
[1]
Question 19
A research group makes a gene inoperative in yeast and compares the mutant strain with a normal strain.
State the name of this technique.
[1]
Explain how this can help infer the function of the gene.
[1]
Question 20
Some model organisms have knockout libraries.
Define a model organism.
[1]
Outline one advantage of using a knockout library.
[1]
Question 21
The graph shows mutation frequency in cultured human cells after exposure to increasing doses of ultraviolet (UV) radiation.
Describe the relationship between UV dose and mutation frequency.
[1]
Identify the UV-dose range in which mutation frequency increases most steeply.
[1]
Suggest how UV radiation can increase mutation frequency.
[1]
Question 22
The diagram compares translation of an original mRNA with translation after a one-base deletion.
State the first codon position after which the amino acid sequence differs.
[1]
Identify the mutation as substitution, insertion or deletion.
[1]
Explain why many amino acids after the mutation differ from the original sequence.
[1]
Question 23
A genetic test reports a single-nucleotide polymorphism associated with a higher risk of a disease. What is the most valid interpretation of the result?
A.
It indicates altered risk and requires interpretation with other evidence.
B.
It shows that the SNP must be in a coding sequence.
C.
It shows that environment cannot affect disease risk.
D.
It proves that the person currently has the disease.
Question 24
In one treatment for sickle-cell disease, a patient’s blood-forming stem cells are edited outside the body and returned to the patient. What type of editing is this?
A.
Germ-line editing intended to alter future generations
B.
Somatic cell editing intended to affect the treated individual
C.
A knockout library produced for model organisms
D.
Natural selection acting on inherited alleles
Question 25
A gene sequence is almost identical in mammals, birds and fish. Which hypothesis best explains this conservation?
A.
The sequence cannot undergo any mutation under any conditions.
B.
Mutations in the sequence are usually selected against because the product is essential.
C.
The species must have identical phenotypes.
D.
The sequence must be non-functional in all species.
Question 26
Two non-coding regions have no known function. Region X shows fewer new mutations than region Y in parent-offspring genome comparisons. What hypothesis could explain conservation of region X?
A.
Region X has a slower mutation rate than region Y.
B.
Region X must code for a longer polypeptide than region Y.
C.
Region X has more insertions and deletions than region Y.
D.
Region X is conserved only because organisms need it to change.
Question 27
Bacteria exposed to an antibiotic may later include resistant mutants.
State why mutation is described as random with respect to benefit.
[1]
Explain why resistant bacteria can become common after antibiotic exposure.
[1]
Question 28
A person receives a commercial genetic test report stating that they carry an SNP associated with increased risk of a common disease.
State why this result is not a diagnosis.
[1]
Suggest two reasons why expert interpretation of the result is important.
[1]
State one possible problem if the result is interpreted without expert advice.
[1]
Question 29
CRISPR-Cas9 can be used to edit a chosen DNA sequence.
State the role of Cas9.
[1]
Explain how guide RNA targets Cas9 to a chosen sequence.
[1]
State the type of bond involved in complementary base pairing between guide RNA and target DNA.
[1]
Question 30
A treatment for beta-thalassaemia edits a patient’s blood-forming stem cells outside the body and returns them to the same patient.
State whether this is somatic or germ-line editing.
[1]
Outline why the edit is not expected to be inherited by the patient’s children.
[1]
State one intended benefit of this treatment.
[1]
Question 31
Potential uses of CRISPR include treating severe disease, editing embryos and altering wild populations.
State one ethical issue raised by genome editing.
[1]
Suggest why embryo editing raises different concerns from somatic editing.
[1]
State why international regulation is difficult.
[1]
Question 32
A DNA sequence in a gene is highly conserved across distantly related vertebrate species.
Define a highly conserved sequence.
[1]
Explain how functional requirements can account for high conservation.
[1]
Question 33
Two DNA regions have similar functions, but one has accumulated fewer mutations over evolutionary time.
State one hypothesis, other than functional requirement, that could explain the difference.
[1]
Suggest two mechanisms that could cause a lower mutation rate in one region.
[1]
Question 34
A table shows four single-base substitutions in a short coding sequence and the amino acid translated from the affected codon.
| Substitution | Original mRNA codon | Mutated mRNA codon | Original amino acid | Mutated product |
|---|---|---|---|---|
| 1 | GAA | GAG | Glu | Glu |
| 2 | UUU | UCU | Phe | Ser |
| 3 | UGG | UGA | Trp | Stop |
| 4 | AAA | AGA | Lys | Arg |
Identify the substitution that is silent.
[1]
Identify the substitution that is nonsense.
[1]
Explain why one substitution can have no effect on the amino acid sequence.
[1]
Suggest why a nonsense mutation is often more harmful than a silent mutation.
[1]
Question 35
The chart shows numbers of mutations detected in different tissues of an adult and in sperm cells from the same individual.
Identify the sample type with the greatest number of detected mutations.
[1]
Distinguish between mutations in sperm cells and mutations in liver cells in terms of inheritance.
[1]
Suggest why a mutation in a cell-cycle control gene in a somatic tissue can have serious consequences.
[1]
Question 36
A knockout library in a model plant was screened for root growth. The table shows root length for wild-type plants and three knockout strains.
| Plant line | Mean root length / mm | Sample size / plants |
|---|---|---|
| Wild type | 48.0 | 20 |
| KO-1 | 41.6 | 20 |
| KO-2 | 29.4 | 20 |
| KO-3 | 44.8 | 20 |
Identify the knockout strain with the greatest reduction in root length compared with wild type.
[1]
Calculate the percentage reduction in root length for this strain.
[1]
Suggest what can be inferred about the knocked-out gene in this strain.
[1]
Question 37
A conserved sequence is found in a regulatory region rather than in a protein-coding region.
State why conservation can occur in non-coding DNA.
[1]
Compare the functional-requirement hypothesis and the slower-mutation-rate hypothesis for sequence conservation.
[1]
Question 38
Replicate bacterial cultures were plated on agar containing an antibiotic. Resistant colonies were counted for each culture.
Describe the variation in numbers of resistant colonies between replicate cultures.
[1]
Suggest why large differences between replicate cultures support the idea that resistance mutations arise before exposure to antibiotic.
[1]
Explain why the antibiotic increases the proportion of resistant bacteria even though it does not direct the mutation.
[1]
Question 39
The diagram shows a CRISPR-Cas9 editing experiment with a guide RNA, target DNA and a donor DNA template.
Identify the molecule that determines the target sequence.
[1]
Explain how this molecule recognizes the target.
[1]
Suggest why some cells show small insertions or deletions instead of the donor-template sequence.
[1]
Question 40
A clinical trial measured fetal haemoglobin in patients before and after CRISPR-Cas9 editing of their blood-forming stem cells.
Describe the overall change in fetal haemoglobin after treatment.
[1]
Identify whether all patients responded equally to treatment.
[1]
Explain why increased fetal haemoglobin can reduce symptoms of haemoglobin disorders.
[1]
State why this treatment is not expected to alter the patients’ children.
[1]
Question 41
A survey asked adults whether they supported three applications of CRISPR: treating a severe somatic disease, editing embryos to prevent disease, and enhancing non-medical traits.
Identify the application with the highest support.
[1]
Describe one difference in support between medical and non-medical applications.
[1]
Suggest two ethical reasons for the difference in support.
[1]
Explain why international harmonization of regulation may be important for embryo editing.
[1]
Question 42
Distinguish between silent, missense and nonsense mutations caused by base substitution.
[1]
Explain how a single base substitution can affect, or fail to affect, the structure and function of a protein.
[1]
Question 43
Outline how the reading frame is used during translation.
[1]
Discuss why insertions and deletions are often more damaging to a polypeptide than base substitutions.
[1]
Question 44
Define gene knockout and knockout library.
[1]
Explain how gene knockout studies in model organisms can be used to investigate gene function.
[1]
Question 45
The graph compares sequence similarity among species for three genomic regions: a coding region, a regulatory region and a non-functional pseudogene.
Identify the region that is most highly conserved.
[1]
Compare the pattern for the pseudogene with the coding region.
[1]
Suggest a functional explanation for high conservation in the regulatory region.
[1]
Suggest one additional type of evidence that would help distinguish functional conservation from a lower mutation rate.
[1]
Question 46
State two causes of gene mutation.
[1]
Evaluate the statement: “Because mutations are random, environmental mutagens do not affect evolution.”
[1]
Question 47
Distinguish between germ cells and somatic cells.
[1]
Discuss consequences of mutations in germ cells and somatic cells for individuals and populations.
[1]
Question 48
Outline the roles of guide RNA and Cas9 in CRISPR-Cas9 editing.
[1]
Explain how CRISPR-Cas9 editing can be used as a somatic treatment for a haemoglobin disorder.
[1]
Question 49
Define conserved sequence and highly conserved sequence.
[1]
Compare and contrast two hypotheses that account for conserved or highly conserved sequences in genes.
[1]
Question 50
Outline two reasons why CRISPR-Cas9 has ethical implications.
[1]
Evaluate the need for international harmonization of regulation for genome editing technologies.
[1]
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