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A4.1.2—Evidence from sequences

Shared molecular systems and sequence comparisons reveal common ancestry, while accumulated DNA, RNA, and protein differences indicate divergence and relatedness.

Syllabus
First assessment 2025
Objective
A4.1.2
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper3
Typical marks2–6

Common command terms

  • Explain
  • Discuss
  • Identify
  • Describe

Scoring notes

Common mistake
Equating sequence similarity with identical whole organisms rather than using it as evidence of recent common ancestry.

Recent exam appearances

November 2024Paper2 ["HL"] · TZ07(b)[ 4 ]A4.1.2—Evidence from sequences
November 2016Paper3 ["HL"] · TZ012(c)(i)[ 1 ]A4.1.2—Evidence from sequences
November 2013Paper3 ["HL"] · TZ01(c)[ 2 ]A4.1.2—Evidence from sequences
November 2013Paper3 ["HL"] · TZ01(b)[ 2 ]A4.1.2—Evidence from sequences
May 2013Paper3 ["HL"] · TZ23[ 6 ]A4.1.2—Evidence from sequences
Practice this objective

Coverage 2012–2024 · Updated 15 Jul 2026

Concept essentials

  • The universality of DNA and the genetic code supports common ancestry among living organisms.
  • Sequence differences accumulate after divergence and can indicate evolutionary distance.
  • Proteins used for comparison must be shared across the organisms being studied.
  • Molecular clocks estimate divergence time from accumulated sequence changes when rates are suitable.
ConceptIB Biology HL