Maternal and paternal chromosomes don't travel as sets
- The idea
- Predict
- See it
- Why
- Check
The idea
“In meiosis I, all the mother's chromosomes go to one pole and all the father's go to the other.”
You got one full set from each parent, so it's natural to picture the sets staying whole. Meiosis I only splits each pair. It ignores which parent a chromosome came from.
The short version
The mistake: In meiosis I, all the mother's chromosomes go to one pole and all the father's go to the other.
What's actually true: Each homologous pair lines up on its own at metaphase I, so each pole usually gets a mix of maternal and paternal chromosomes.
- Each homologous pair has one chromosome from the mother and one from the father. In meiosis I, the two go to opposite poles.
- Which way a pair faces at metaphase I is random. It doesn't depend on the other pairs. This is independent assortment.
- With 23 pairs, one person can make about 8 million chromosome combinations in their gametes.
On the exam: Each homologous pair faces its own way at metaphase I. Nothing keeps one parent's set together.