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A3.1.6—Diversity in chromosome numbers

Chromosome numbers are usually constant within a species but vary widely between species without measuring complexity, evolutionary progress, or organism type.

Syllabus
First assessment 2025
Objective
A3.1.6
Level
SL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1

Common command terms

  • State

Scoring notes

Common mistake
Treating chromosome number as a measure of organism complexity or evolutionary progress.

Recent exam appearances

November 2025Paper1B ["SL"] · TZ11(a)(ii)[ 1 ]A3.1.6—Diversity in chromosome numbers
May 2019Paper1 ["SL"] · TZ113[ 1 ]A3.1.6—Diversity in chromosome numbers
November 2018Paper1 ["SL"] · TZ012[ 1 ]A3.1.6—Diversity in chromosome numbers
November 2016Paper2 ["SL"] · TZ04(a)[ 1 ]A3.1.6—Diversity in chromosome numbers
November 2016Paper1 ["SL"] · TZ014[ 1 ]A3.1.6—Diversity in chromosome numbers
Practice this objective

Coverage 2016–2025 · Updated 15 Jul 2026

Concept essentials

  • Diploid chromosome number is usually constant within a species.
  • Haploid cells contain one chromosome from each homologous pair.
  • Autosomes exclude sex chromosomes.
  • Different species can have very different chromosome numbers without differing in complexity.
ConceptIB Biology SL