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D2.1.11—Meiosis generates variation

Meiosis generates variation through crossing over, random bivalent orientation, independent assortment and random fertilization in sexual reproduction and inheritance patterns.

Syllabus
First assessment 2025
Objective
D2.1.11
Level
SL

Exam analysis

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

Common command terms

  • State
  • Explain
  • Describe
  • Draw
  • Outline
  • Identify

Scoring notes

Common mistake
Saying crossing over occurs between sister chromatids instead of non-sister chromatids of homologous chromosomes.

Recent exam appearances

May 2024Paper2 ["SL"] · TZ26(c)[ 7 ]D2.1.11—Meiosis generates variation
November 2015Paper1 ["SL"] · TZ013[ 1 ]D2.1.11—Meiosis generates variation
May 2014Paper2 ["SL"] · TZ13(a)(i)[ 1 ]D2.1.11—Meiosis generates variation
May 2014Paper1 ["SL"] · TZ210[ 1 ]D2.1.11—Meiosis generates variation
May 2011Paper1 ["SL"] · TZ115[ 1 ]D2.1.11—Meiosis generates variation
Practice this objective

Coverage 2011–2024 · Updated 16 Jul 2026

Meiosis Creates Variation through Pairing and Recombination

Meiosis generates genetic diversity through random orientation of bivalents and crossing over between non-sister chromatids.

At metaphase I, each bivalent can face either pole independently. The maternal and paternal homologues therefore segregate into many possible whole-chromosome combinations.

During prophase I, non-sister chromatids of homologous chromosomes exchange corresponding DNA at chiasmata, producing recombinant chromatids with new combinations of linked alleles.

One gamete can receive a maternal chromosome carrying a short paternal segment after crossing over, plus a different random mixture of the remaining maternal and paternal homologues.

Random fertilization adds further variation but is not a meiotic process. Meiosis does not direct combinations toward future advantage.

Meiosis generates variation

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using State / Explain / Describe.

Command terms

State / Explain / Describe / Draw / Outline / Identify

What earns marks

Build the answer around this relationship: Crossing over exchanges DNA between non-sister chromatids of homologous chromosomes.

Watch for

Saying crossing over occurs between sister chromatids instead of non-sister chromatids of homologous chromosomes.

Representative question

Question 1

[Maximum number: 7]

Explain the stages and processes of meiosis leading to genetic variation.

Core Cell Division

  • Cell division produces daughter cells for growth, repair or reproduction; cytokinesis divides cytoplasm by a contractile ring in animals or a cell plate in plants.
  • DNA replication creates sister chromatids joined at centromeres before nuclear division.
  • Mitosis preserves chromosome number: chromosomes condense, align, sister chromatids separate and nuclei reform, producing genetically identical nuclei.
  • Meiosis follows one replication with two divisions: homologous chromosomes separate in meiosis I and sister chromatids in meiosis II, producing haploid cells.
  • Crossing over, independent orientation and random fertilization generate allele combinations.
  • Non-disjunction is failed chromosome separation and can produce aneuploid cells, including trisomy 21.
  • Identify stages in micrographs from chromosome condensation, equatorial alignment, separation and nuclear-envelope cues.

Concept essentials

  • Crossing over exchanges DNA between non-sister chromatids of homologous chromosomes.
  • Chiasmata are visible points associated with crossing over.
  • Random orientation of bivalents produces different chromosome combinations.
  • Random fertilization adds further genetic variation in sexual reproduction.