Nondisjunction in meiosis I spoils all four gametes
- The idea
- Predict
- See it
- Why
- Check
The idea
“Nondisjunction gives the same abnormal gametes in either division.”
Up close, both errors look the same. Two chromosomes go to one pole. Timing decides how many gametes end up wrong.
The short version
The mistake: Nondisjunction gives the same abnormal gametes in either division.
What's actually true: If a pair fails to separate in meiosis I, all four gametes are abnormal. A meiosis II failure spoils only two.
- Nondisjunction means chromosomes fail to separate. In meiosis I it's a homologous pair. In meiosis II it's two sister chromatids.
- A meiosis I error comes before the cell splits, so one cell is n + 1 and the other is n - 1. Meiosis II passes each count to two gametes.
- A meiosis II error happens in only one of the two cells, which makes an n + 1 and an n - 1 gamete. The other cell makes two normal ones.
On the exam: After one nondisjunction, zero normal gametes means meiosis I and two means meiosis II.