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IB Biology HL A3.2.5 Molecular clocks Question Bank

Practise IB Biology HL A3.2.5 by relating sequence substitutions to divergence time and interpreting molecular evidence in cladograms.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Relate a greater number of sequence substitutions to a greater time since divergence.
  • Use cytochrome c sequence differences to compare evolutionary distances between chordates.

A3.2.5 (HL)—Molecular clock question 1

[Maximum number: 1]

The evolutionary clock estimates the time elapsed since species separated from a common ancestor based on fossil evidence. The graph shows the number of differences in the DNA sequences (nucleotide substitutions) coding for certain polypeptides in 11 closely related mammals.

Figure for Question A3.2.5 (HL)—Molecular clock question 1 — IB Biology HL

State the relationship between divergence time and number of substitutions.

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