Mixing up the stages of mitosis
- The idea
- Predict
- See it
- Why
- Check
The idea
“The sisters split in metaphase, and the nuclear envelope breaks down later, around anaphase.”
The stage names sound alike, and so do the pictures. The order gets easier once you see that each event sets up the next.
The short version
The mistake: The sisters split in metaphase, and the nuclear envelope breaks down later, around anaphase.
What's actually true: The envelope breaks down before the chromosomes line up, sisters split only in anaphase, and new envelopes form in telophase.
- Each chromosome is two sister chromatids, identical copies made in S phase. The spindle forms outside the nucleus and can't reach them until the envelope breaks down.
- That breakdown is prometaphase, or late prophase in some books. Fibers then attach at kinetochores, protein patches on each centromere.
- In anaphase the cell briefly has twice as many chromosomes, with the same amount of DNA. Cytokinesis usually overlaps telophase and makes two daughter cells.
On the exam: The envelope breaks down before the line-up, and the sisters split only in anaphase.