Homologs split only in anaphase I
- The idea
- Predict
- See it
- Why
- Check
The idea
“Homologs pair at metaphase, or they have already separated once they pair or line up.”
The same pair of chromosomes is busy in every stage, so the stages blur. And a pair lined up across the middle, one partner on each side, already looks split.
The short version
The mistake: Homologs pair at metaphase, or they have already separated once they pair or line up.
What's actually true: Homologs pair and cross over in prophase I, line up as pairs in metaphase I, and separate only in anaphase I.
- In prophase I, homologs pair along their length. This is called synapsis, and crossing over happens while they are joined.
- In metaphase I, spindle fibers from opposite poles attach to the partners at the middle. They are still together.
- In anaphase I, the fibers pull the partners to opposite poles. Each partner keeps both sister chromatids until anaphase II, in meiosis II.
On the exam: Prophase I pairs, metaphase I lines up, anaphase I pulls apart. Lining up isn't splitting up.