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D2.1.6—Shared features

Mitosis and meiosis share chromosome condensation, spindle microtubule movement and chromatid separation, although their outcomes differ strongly in dividing cells.

Syllabus
First assessment 2025
Objective
D2.1.6
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2021
Most common paperPaper1
Typical marks1

Common command terms

  • Identify

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May 2021Paper1 ["HL"] · TZ235[ 1 ]D2.1.6—Shared features

Coverage 2021–2021 · Updated 16 Jul 2026

Condensation and Spindle Forces Make Chromosomes Movable

Each chromosome is one very long DNA molecule. Accurate division requires it to be packaged into a compact unit and attached to machinery that can position and separate it.

Mitosis and meiosis share three mechanical features:

  • DNA wrapped around histones and nucleosomes condenses into chromosomes.
  • Spindle microtubules attach through centromere-associated structures.
  • Microtubule dynamics and motor proteins position and move chromosomes.

Condensation does not copy DNA. It changes packaging so long molecules can move with less tangling or breakage.

DNA wraps around histones into chromatin, condenses into a duplicated chromosome and attaches at the centromere region to spindle microtubules.

Reconstruct How One Replicated Cell Becomes Two Daughter Cells

DNA replication creates joined sister chromatids → chromosomes condense and attach to the spindle → metaphase alignment checks bipolar attachment → sister chromatids separate → two nuclei re-form → cytokinesis partitions the cytoplasm

Continuity requirement What supplies it
complete genome in each nucleus replication followed by equal chromatid separation
controlled chromosome movement condensation, spindle microtubules and motor proteins
two separate cells animal cleavage furrow or plant cell plate
suitable daughter-cell contents equal or functionally unequal cytoplasmic partition

To identify a stage, prioritize chromosome position and nuclear-envelope state. To explain the outcome, connect those observations to what is being separated.

Meiosis I Separates Homologues; Meiosis II Separates Chromatids

A bivalent is a paired set of duplicated homologous chromosomes: one maternal homologue and one paternal homologue, each made of two sister chromatids.

Question Meiosis I Meiosis II
what aligns? bivalents individual duplicated chromosomes
what separates? homologous chromosomes sister chromatids
do centromeres divide? no yes
chromosome-number effect diploid → haploid remains haploid

Use the object being separated in explanations: homologues move apart in anaphase I; sister chromatids move apart in anaphase II.

Calling both events 'chromosomes separating' hides the reason meiosis I is the reduction division.

Track What Separates to Explain Reduction, Error and Variation

Event What changes Main consequence
replication before meiosis each chromosome gains a sister chromatid DNA prepared for two divisions
meiosis I homologous chromosomes separate chromosome number is halved
meiosis II sister chromatids separate four haploid products can form
non-disjunction one required separation fails aneuploid gametes may form

Variation is layered: crossing over recombines alleles within chromosomes, random orientation assort homologues independently, and random fertilization combines two independently produced gametes.

When explaining any meiotic outcome, name the stage, the chromosome object that should separate, the chromosome number before and after, and whether the result changes number, allele combination or both.

Shared features

[ 1 ]

What occurs in cell division during both mitosis and meiosis?

Concept essentials

  • Both mitosis and meiosis use spindle microtubules to move chromosomes.
  • Sister chromatids separate in mitosis and meiosis II.
  • Chromosome condensation helps make DNA movable during division.
  • Crossing over and homologous pairing are not shared features of mitosis.