D2.2 Gene expression
Practice exam-style IB Biology questions for Gene expression, aligned with the syllabus and grouped by topic.
Question 1
A gene codes for an enzyme that catalyses one step in pigment synthesis. What sequence best links this gene to the phenotype?
A.
Enzyme activity → DNA base sequence → transcription → translation → pigment phenotype
B.
DNA base sequence → translation → transcription → enzyme activity → pigment phenotype
C.
DNA base sequence → transcription → translation → enzyme activity → pigment phenotype
D.
DNA base sequence → pigment phenotype → transcription → translation → enzyme activity
Question 2
What enables transcription factors to regulate different genes selectively?
A.
They remove introns from pre-mRNA after RNA polymerase has finished transcription.
B.
They bind to specific base sequences in DNA near or within regulatory regions.
C.
They hydrolyse all mRNA molecules with the same efficiency in the cytoplasm.
D.
They alter the amino acid sequence of histone proteins during translation.
Question 3
What is the role of a promoter in transcription?
A.
It is a protein that degrades mRNA after translation.
B.
It is an RNA sequence that binds ribosomes to start translation.
C.
It is a DNA sequence where RNA polymerase and associated proteins assemble to start transcription.
D.
It is a methyl group that permanently changes a coding sequence.
Question 4
The degradation rate of an mRNA coding for a hormone receptor increases. What is the most likely direct effect?
A.
More receptor polypeptides are synthesized from that mRNA.
B.
Fewer receptor polypeptides are synthesized from that mRNA.
C.
The DNA sequence of the receptor gene is changed.
D.
RNA polymerase is unable to bind to all promoters.
Question 5
During epigenesis, cells in an embryo become increasingly specialized. What changes during this process?
A.
All genes become expressed at the same rate in every cell.
B.
Different cell types lose all genes that they no longer require.
C.
Patterns of gene expression change without changing the DNA base sequence.
D.
The genetic code changes in each tissue.
Question 6
What is the usual effect of methylation of cytosine in a gene promoter?
A.
The cytosine base is replaced by adenine in the DNA sequence.
B.
The promoter becomes an exon in the mature mRNA.
C.
The downstream gene is translated directly from DNA.
D.
Transcription of the downstream gene is repressed.
Question 7
Define gene expression.
[1]
Outline how expression of a gene coding for an enzyme can affect phenotype.
[1]
Question 8
An enhancer is located far upstream of a gene but increases transcription of that gene. What explains this effect?
A.
The enhancer is copied into every mRNA made by the gene.
B.
The enhancer is translated into a polypeptide that binds the ribosome.
C.
DNA looping can bring an activator bound to the enhancer near the promoter.
D.
The enhancer prevents all transcription factors from binding DNA.
Question 9
What is the usual effect of a longer poly-A tail on a eukaryotic mRNA molecule?
A.
The mRNA becomes part of the genome.
B.
The mRNA is immediately degraded by DNA polymerase.
C.
The mRNA cannot bind to ribosomes because adenine prevents translation.
D.
The mRNA is more stable and can be translated for longer.
Question 10
Which description correctly distinguishes the transcriptome from the genome of a liver cell?
A.
The transcriptome is inherited unchanged through meiosis; the genome changes each minute.
B.
The transcriptome is all proteins in the cell; the genome is all RNA molecules in the cell.
C.
The transcriptome is the set of RNA transcripts present at a particular time; the genome is the complete DNA information.
D.
The transcriptome contains all genes that are not expressed; the genome contains only expressed genes.
Question 11
What is a possible effect of methylation of amino acids in histone tails?
A.
It always changes the nucleotide sequence of the gene being regulated.
B.
It can repress or activate transcription by changing access to chromatin.
C.
It prevents histones from associating with DNA in all eukaryotic cells.
D.
It converts mRNA into DNA before translation occurs.
Question 12
What is meant by epigenetic inheritance during mitosis?
A.
Daughter cells inherit only the mRNA molecules present before mitosis.
B.
Daughter cells receive different genetic codes from the same parent cell.
C.
Daughter cells inherit new alleles produced by methylation of cytosine bases.
D.
Daughter cells maintain patterns of gene expression because some epigenetic tags remain in place or are copied.
Question 13
Air pollution can affect gene expression in exposed cells. What mechanism is included as an example in this topic?
A.
Immediate deletion of all genes used in inflammation.
B.
Replacement of all promoter sequences by particulate matter.
C.
Alteration of methyl tags on DNA affecting genes involved in cell responses.
D.
Conversion of differentiated cells into gametes by nitrogen oxides.
Question 14
Why are monozygotic twins useful for investigating environmental effects on gene expression?
A.
They are produced from two different eggs fertilised by two different sperm.
B.
They inherit no epigenetic tags from either parent.
C.
They have essentially the same genome, so differences can indicate environmental or epigenetic effects.
D.
They always have identical transcriptomes throughout life.
Question 15
The diagram shows a regulatory region of a eukaryotic gene.
Identify the roles of the promoter and enhancer in transcription regulation.
[1]
Explain how a transcription factor can increase transcription of this gene.
[1]
Question 16
State the enzyme type responsible for mRNA degradation.
[1]
Explain how increasing the rate of degradation of a specific mRNA regulates translation.
[1]
Question 17
State what is meant by differentiation.
[1]
Distinguish between an epigenetic change and a mutation.
[1]
Question 18
Two cells from the same person, a pancreatic β cell and a skin cell, are compared.
Compare their genomes.
[1]
Explain why their transcriptomes and proteomes differ.
[1]
Question 19
Distinguish between monozygotic and dizygotic twins.
[1]
State why monozygotic twins are useful in studies of the environment and gene expression.
[1]
Question 20
Define proteome.
[1]
Explain why the proteome is not always a direct copy of the transcriptome.
[1]
Question 21
A study measured promoter methylation and relative mRNA abundance for gene A in cultured human cells.
Describe the relationship shown between promoter methylation and mRNA abundance.
[1]
Explain the relationship using your knowledge of gene expression.
[1]
Suggest one reason why mRNA abundance is not zero even at high promoter methylation.
[1]
Question 22
Expression of three lac operon genes was measured in Escherichia coli grown with glucose only or with lactose only.
Identify the carbon source associated with higher expression of lac genes.
[1]
Explain the role of lactose in producing this result.
[1]
State why the three genes show a similar expression pattern.
[1]
Question 23
Most epigenetic tags are removed from gametes, but some remain. What consequence can result?
A.
The base sequence of every imprinted gene is rewritten after fertilization.
B.
Expression of an allele can depend on whether it was inherited from the mother or father.
C.
All recessive alleles are removed from the ovum before meiosis.
D.
All offspring become genetically identical to the father.
Question 24
How can oestrogen increase expression of the progesterone receptor gene in uterine lining cells?
A.
Oestrogen binds directly to ribosomes and changes the genetic code.
B.
Oestrogen binds an intracellular receptor and the complex regulates transcription of target genes.
C.
Oestrogen removes the progesterone receptor gene from all non-target cells.
D.
Oestrogen digests the mRNA for the progesterone receptor gene.
Question 25
In the lac operon of Escherichia coli, lactose is present. What happens to expression of genes for lactose use?
A.
Lactose is translated into enzymes for its own breakdown.
B.
Lactose methylates all coding sequences, causing permanent mutation.
C.
Lactose inactivates the repressor, allowing transcription of lac genes.
D.
Lactose activates the repressor, preventing all transcription of lac genes.
Question 26
State what is meant by methylation.
[1]
Explain the effect of promoter methylation on expression of a downstream gene.
[1]
State one possible effect of histone methylation.
[1]
Question 27
A liver cell divides by mitosis to replace damaged tissue.
Outline how epigenetic inheritance helps the daughter cells remain liver cells.
[1]
State why this is not inheritance of a new allele.
[1]
Question 28
Pregnant individuals exposed to high air pollution show altered DNA methylation in placental cells.
State one type of pollutant that may be present in polluted air.
[1]
Suggest how altered methylation could affect development of the embryo or fetus.
[1]
Question 29
Ligers result from a male lion and female tiger, whereas tigons result from a male tiger and female lion.
State what genomic imprinting means.
[1]
Outline why ligers and tigons can differ in growth despite both being lion–tiger hybrids.
[1]
Question 30
Oestrogen affects cells of the uterine lining.
State why oestrogen can enter target cells.
[1]
Explain how oestrogen can change expression of the progesterone receptor gene.
[1]
Question 31
The diagram shows the lac operon in Escherichia coli when lactose is absent and when lactose is present.
State what an operon is.
[1]
Explain how lactose affects transcription of the lac genes.
[1]
Question 32
The mRNA for protein X persists for several days, whereas the mRNA for protein Y persists for only minutes.
Predict which protein can continue to be synthesized for longer if transcription stops.
[1]
Explain the prediction.
[1]
Question 33
Define phenotypic plasticity.
[1]
Outline how environmental conditions can produce different phenotypes from the same genotype.
[1]
Question 34
Cells were treated with a chemical that shortens the poly-A tail of mRNA for protein B. Protein B concentration was measured over time.
State the effect of the treatment on protein B concentration.
[1]
Explain how shortening the poly-A tail could cause this effect.
[1]
Suggest why transcription rate was also measured in the study.
[1]
Question 35
DNA methylation similarity was compared in monozygotic twin pairs living together or apart.
Compare methylation similarity in twins living together and twins living apart.
[1]
Explain why monozygotic twins were used in this study.
[1]
Suggest one limitation of using twin studies to infer environmental effects on gene expression.
[1]
Question 36
Uterine lining cells were cultured with different concentrations of oestrogen. Expression of the progesterone receptor gene was measured.
Describe the effect of oestrogen concentration on progesterone receptor mRNA.
[1]
Explain how oestrogen produces this effect.
[1]
Suggest why receptor protein was measured as well as mRNA.
[1]
Question 37
A reporter gene was placed under control of a promoter alone or a promoter plus an enhancer. The enhancer-binding site was then mutated.
Identify the construct with highest reporter expression.
[1]
Explain the effect of adding the enhancer.
[1]
Explain the effect of mutating the enhancer-binding site.
[1]
Question 38
A mutation changes a base sequence in an enhancer but does not alter the coding sequence of the gene.
Suggest how this mutation could reduce production of the protein.
[1]
State why the amino acid sequence of the protein would not necessarily be changed.
[1]
Question 39
RNA and protein abundance for four genes were measured in the same cell type.
| Gene | mRNA abundance / a.u. | Protein abundance / a.u. |
|---|---|---|
| Gene A | 82 | 18 |
| Gene B | 24 | 76 |
| Gene C | 65 | 61 |
| Gene D | 31 | 34 |
Identify the gene for which mRNA abundance is least predictive of protein abundance.
[1]
Describe one pattern shown by the data.
[1]
Explain two reasons why protein abundance may not match mRNA abundance.
[1]
Suggest why measurements were made at the same time point.
[1]
Question 40
Researchers measured DNA methylation of an inflammation-related gene in airway cells from people exposed to low or high particulate air pollution.
| Exposure group | n | Promoter methylation / % (mean ± SD) | mRNA abundance / relative units (mean ± SD) |
|---|---|---|---|
| Low particulate | 30 | 64 ± 8 | 1.0 ± 0.3 |
| High particulate | 30 | 43 ± 10 | 2.4 ± 0.7 |
Describe the effect of high particulate exposure on methylation and mRNA abundance.
[1]
Suggest how the methylation change could affect airway phenotype.
[1]
Evaluate whether these data alone prove that pollution caused the expression change.
[1]
Question 41
Growth-related gene expression was compared in lion–tiger hybrids. Gene G is normally expressed only from the paternal allele.
| Hybrid | Mother | Father | Maternal G allele | Paternal G allele |
|---|---|---|---|---|
| Liger | Tiger | Lion | Silent | Expressed |
| Tigon | Lion | Tiger | Silent | Expressed |
State which parental allele of gene G is expressed according to the table.
[1]
Compare predicted expression of gene G in a liger and a tigon.
[1]
Explain why this is an epigenetic rather than Mendelian dominant–recessive effect.
[1]
Question 42
Outline the stages by which information in a gene can produce a protein product.
[1]
Explain how regulation of gene expression can produce different phenotypes in cells with the same genome.
[1]
Question 43
Single-cell RNA sequencing was used to follow cells during early development. Cells were grouped by similarity of their transcriptomes.
Describe the change in transcriptome diversity during development.
[1]
Explain how this supports epigenesis.
[1]
Suggest one additional measurement that would strengthen the conclusion that differentiation is regulated epigenetically.
[1]
State one limitation of using transcriptomes alone to infer cell phenotype.
[1]
Question 44
Define promoter, enhancer and transcription factor.
[1]
Explain how proteins binding to specific DNA base sequences can activate or inhibit transcription.
[1]
Question 45
State two examples of epigenetic tags included in this topic.
[1]
Discuss how methylation can regulate gene expression without changing the genotype.
[1]
Question 46
Outline how epigenetic inheritance can occur during mitosis.
[1]
Evaluate the claim that epigenetic inheritance is the same as inheritance of a mutation.
[1]
Question 47
Define phenotypic plasticity and give one environmental factor that can affect gene expression.
[1]
Discuss how environmental factors can alter gene expression and phenotype, using air pollution as one example.
[1]
Question 48
Explain why monozygotic twins are useful in studies of gene expression.
[1]
Evaluate how twin studies can be used to investigate environmental effects on gene expression.
[1]
Question 49
Outline how oestrogen affects gene expression in target cells.
[1]
Compare and contrast regulation of gene expression by oestrogen in human cells and by lactose in Escherichia coli.
[1]
Question 50
Outline why most epigenetic tags are removed from gametes.
[1]
Compare and contrast inheritance of imprinted genes with Mendelian inheritance, referring to ligers and tigons.
[1]
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