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D2.1.3—Equal and unequal cytokinesis

Cytokinesis is usually equal, but budding and oogenesis can distribute cytoplasm unequally between daughter cells in specific reproductive contexts and development.

Syllabus
First assessment 2025
Objective
D2.1.3
Level
HL

Cytokinesis Can Partition Cell Contents Unequally

Cytokinesis is usually equal, but unequal cytokinesis can give daughter cells very different amounts of cytoplasm.

Whatever their final sizes, both daughters must receive at least one mitochondrion and any other organelle that can arise only by growth and division of a pre-existing organelle.

Example Partitioning result
Typical equal cytokinesis Daughters receive similar shares of cytoplasm
Human oogenesis One large ovum retains most cytoplasm; small polar bodies receive little
Yeast budding A smaller bud separates from the larger parent cell

Unequal cytoplasm does not mean unequal nuclear DNA: chromosomes can still be segregated correctly before asymmetric cytokinesis.

Equal and unequal cytokinesis

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Identify.

Command terms

Identify

What earns marks

Build the answer around this relationship: Equal cytokinesis gives daughter cells similar cytoplasmic volumes.

Representative question

Question 1

[Maximum number: 1]

Daughter cells usually receive equal amounts of cytoplasm as parent cells undergo cytokinesis. Which of the following is an exception?

A

Asexual reproduction by budding in yeast

B

Bacterial cell division

C

Cloning of lymphocytes during an immune response

D

Formation of a zygote during fertilization

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

  • Equal cytokinesis gives daughter cells similar cytoplasmic volumes.
  • Yeast budding is an example of unequal cytokinesis.
  • Oogenesis uses unequal cytokinesis to retain cytoplasm in the ovum.
  • Cytokinesis pattern affects daughter-cell size and resources.