CourseCourseQ BankQuestion BankDocsDocuments

D2.2.8 (HL)—Environmental effects on expression

Environmental factors can alter gene expression through signalling, transcript changes and epigenetic modifications such as DNA methylation in cells and organisms.

Syllabus
First assessment 2025
Objective
D2.2.8
Level
HL

Exam analysis

Chance of appearing3%of analysed past papers
Latest appearanceMay 2018
Most common paperPaper2
Typical marks1–3

Common command terms

  • Compare
  • Suggest
  • Discuss

Scoring notes

Common mistake
Treating altered expression as a necessary DNA base-sequence mutation.

Recent exam appearances

May 2018Paper1 ["HL"] · TZ211[ 1 ]D2.2.8 (HL)—Environmental effects on expression
May 2018Paper2 ["HL"] · TZ21(e)[ 3 ]D2.2.8 (HL)—Environmental effects on expression
May 2017Paper2 ["HL"] · TZ11(f)(ii)[ 2 ]D2.2.8 (HL)—Environmental effects on expression
Practice this objective

Coverage 2017–2018 · Updated 16 Jul 2026

Air Pollution Can Alter Epigenetic Gene Regulation

HL only

Environmental exposure can alter gene expression by changing epigenetic tags; air pollution can modify DNA and histone methylation patterns.

Pollutants reaching lung tissue can trigger cellular responses associated with altered methylation. Changed access to regulated genes can affect inflammatory pathways and may contribute to lung disease without changing the DNA sequence.

Air-pollution exposure → altered DNA or histone methylation → altered transcription pattern → changed cell response → possible contribution to inflammation or respiratory disease.

Comparing exposed and less-exposed lung-cell samples may reveal different methylation and expression patterns associated with inflammatory responses.

An association between pollution, methylation and disease does not by itself prove that one methylation change caused the disease; exposure, dose and alternative causes must be evaluated.

Environmental effects on expression

HL only

Assessment in practice

1–3 marks
How it is assessed

This objective is assessed through essay response, multiple choice, commonly using Compare / Suggest / Discuss.

Command terms

Compare / Suggest / Discuss

What earns marks

Build the answer around this relationship: Environmental conditions can alter gene expression.

Watch for

Treating altered expression as a necessary DNA base-sequence mutation.

Representative question

Question 1

[Maximum number: 3]

Using the data in the bar chart, discuss the evidence for Arabidopsis plants adapting to different daylight regimes by changing the pattern of gene expression.

HL Gene Expression Control

HL only
  • Transcription factors, promoters, enhancers, activators and repressors control RNA polymerase activity.
  • mRNA lifetime limits translation; poly-A shortening and nucleases help remove transcripts.
  • DNA methylation and histone modification alter chromatin access without changing base sequence, creating epigenetic patterns during differentiation.
  • The genome is all genetic information; the transcriptome and proteome vary with cell type, time and environment.
  • Some epigenetic marks persist through cell division or inheritance, although most are reset during gamete formation; genomic imprinting is an exception.
  • Hormones regulate eukaryotic transcription through receptors and transcription factors; lac and trp operons illustrate bacterial control.
  • Twin studies and environmental exposures help separate genetic, epigenetic and environmental effects on phenotype.

Concept essentials

  • Environmental conditions can alter gene expression.
  • Changes in mRNA abundance show altered transcription or transcript level.
  • DNA methylation patterns can be changed by environmental factors.
  • Different light regimes can produce different transcript patterns in plants.