Mitosis produces two genetically identical nuclei.

This figure summarizes the stages of mitosis with labeled drawings and accompanying micrographs. The anaphase panel shows sister chromatids separating and moving toward opposite poles along spindle microtubules, while the telophase panel shows chromosomes arriving at the poles as the nuclear envelope reforms. It provides a visual “before/after” for chromosome segregation versus nuclear reassembly. Source

Anaphase and telophase are the late stages that physically separate duplicated chromosomes and then rebuild nuclear structures so each future daughter cell receives a complete genome.

Anaphase: separating sister chromatids

Key idea and main events

Anaphase begins when the cell commits to chromosome separation: the duplicated chromosomes are pulled apart so each pole receives one copy of every chromosome. As required by the syllabus, spindle fibers separate sister chromatids toward opposite poles.

Structures that make movement possible

The mitotic spindle is a dynamic microtubule-based machine that attaches to chromosomes and generates force.

Fluorescence microscopy image of a mitotic spindle highlighting the main components that drive chromosome movement: microtubules (spindle fibers), condensed chromosomes (DNA), and kinetochores. The kinetochore signals where spindle microtubules attach to each chromatid, enabling pulling forces during anaphase. This reinforces how structural organization at the centromere translates into reliable chromatid segregation. Source

Chromosomes are moved by coordinated actions at kinetochores and along spindle microtubules.

Mechanism of chromatid separation

Anaphase can be understood as two linked processes: separating chromatids and increasing pole-to-pole distance.

• Cohesion is released

  • The proteins that hold sister chromatids together are cleaved, allowing the chromatids to become independent chromosomes.

• Kinetochore microtubules shorten (pulling)

  • Microtubules attached to kinetochores depolymerize, shortening as they reel chromatids toward opposite poles.

  • Motor proteins at kinetochores can “walk” chromosomes along microtubules, reinforcing directed movement.

• Spindle elongation (pushing and sliding)

  • Non-kinetochore microtubules overlap in the cell center and slide past each other, while additional polymerization can maintain overlap.

  • This increases the distance between poles, helping segregate chromosome sets into distinct regions.

Observable outcomes

By late anaphase:

• The separated chromosomes are clustered near opposite poles.

• The cell’s internal organization becomes clearly bipolar, reducing the chance that chromosomes mix between future nuclei.

Telophase: rebuilding nuclei and dismantling the spindle

Reversal and reassembly

Telophase reorganizes the cell from a spindle-driven state back toward a typical interphase-like nuclear architecture. As required by the syllabus, the spindle breaks down and new nuclear envelopes develop.

Key telophase events include:

• Spindle disassembly

  • Microtubules depolymerize and spindle-associated proteins disengage, eliminating the structures used for chromosome movement.

• Nuclear envelope re-formation

  • Membrane vesicles and nuclear envelope components associate around each chromosome set, producing two separate nuclei.

• Chromosome decondensation

  • Highly compacted chromosomes begin to uncoil into less condensed chromatin, supporting future gene expression.

• Nucleolus reappears

  • Nucleolar components reassemble, restoring ribosomal RNA synthesis capacity within each nucleus.

Functional significance

Telophase ensures that:

• Each pole’s chromosome set is enclosed by its own nuclear envelope, physically separating the genomes.

• The cell transitions away from chromosome transport and toward normal nuclear function, setting the stage for cytoplasmic division to complete cell separation.