Practice IB Biology Topic D2.2 Gene Expression with authentic exam-style questions for both SL and HL students. This question bank focuses on the exact syllabus content for D2.2 Gene Expression and mirrors Paper 1A, 1B, 2 style where relevant.
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A person has a mutation that leaves an enzyme correctly made but unable to fold into its working shape, so the trait it controls is altered.
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A reporter gene is tested with different regulatory DNA and proteins.
| Construct | Repressor protein present | Transcription rate |
|---|
| promoter only | no | 100 units |
| promoter + silencer | no | 98 units |
| promoter + silencer | yes | 12 units |
| promoter + mutated silencer | yes | 96 units |
Which conclusion is best supported?
Epigenetic mechanisms can regulate gene expression in development, physiology and responses to the environment.
(a) the consequences of genomic imprinting in lion–tiger hybrids, explaining the origin of size differences between ligers and tigons.
(b) how environmental pollutants, such as air pollution, can influence the epigenetic regulation of immune response genes.
(c) the mechanism by which oestrogen regulates gene expression related to endometrial development and maintenance in the uterine cycle.
In the image below, the left panel shows changes in global DNA methylation levels (%) in somatic cells over three generations ( to ) following an environmental stimulus in the generation. The right panel displays the expression level of a phenotypic trait over six generations ( to ), highlighting how the phenotype changes across generations despite no changes in the DNA sequence.
(c) how DNA methylation can be involved in the heritable silencing of gene expression.
(d) how epigenetic changes, such as those shown here, can contribute to phenotypic plasticity without altering the DNA sequence.
Figure showing transcriptional regulation of gene in a eukaryotic cell.
(a) the function of the promoter shown in the figure.
(b) the role of (i) transcription factors and (ii) mediator proteins in this diagram.
(d) one reason why this regulatory mechanism allows differential gene expression in different cell types.
The repressor binds a specific silencer sequence and reduces transcription.
The silencer prevents RNA degradation only when the repressor is absent.
The promoter inhibits transcription when the silencer sequence is mutated.
The repressor increases transcription by binding directly to the promoter.
(a) the trend in global DNA methylation (%) from to .
(b) the generation in which the phenotypic trait expression peaks. a possible epigenetic explanation for why expression peaks at that generation.
(c) how the enhancer and its associated proteins regulate the transcription of gene .
