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A4.1.7—Reproductive isolation and differential selection

Reproductive isolation stops gene flow, allowing different selection pressures and genetic changes to drive populations along separate evolutionary paths toward speciation.

Syllabus
First assessment 2025
Objective
A4.1.7
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2024
Most common paperPaper1
Typical marks1–3

Common command terms

  • Identify
  • Analyse
  • State
  • Describe
  • Outline
  • Distinguish
  • Explain

Scoring notes

Common mistake
Listing a barrier but not connecting it to reduced gene flow.

Recent exam appearances

May 2024Paper2 ["HL"] · TZ17(c)[ 7 ]A4.1.7—Reproductive isolation and differential selection
November 2022Paper1 ["HL"] · TZ036[ 1 ]A4.1.7—Reproductive isolation and differential selection
May 2018Paper1 ["HL"] · TZ117[ 1 ]A4.1.7—Reproductive isolation and differential selection
May 2017Paper2 ["HL"] · TZ27(a)[ 3 ]A4.1.7—Reproductive isolation and differential selection
November 2012Paper3 ["HL"] · TZ0D2(a)(ii)[ 1 ]A4.1.7—Reproductive isolation and differential selection
Practice this objective

Coverage 2012–2024 · Updated 15 Jul 2026

Concept essentials

  • Reproductive isolation reduces or prevents gene flow between populations.
  • Temporal, behavioural and geographic barriers can separate gene pools.
  • Different selection pressures can favour different adaptations in isolated populations.
  • Speciation is supported when divergence prevents successful fertile interbreeding.
ConceptIB Biology HL