Meiosis halves and shuffles the chromosomes
- The idea
- Predict
- See it
- Why
- Check
The idea
“Meiosis copies the cell, so the new cells keep the same chromosome number and alleles.”
Meiosis uses mitosis's words, like prophase, spindle and chromatids. So it's easy to assume it makes copies too.
The short version
The mistake: Meiosis copies the cell, so the new cells keep the same chromosome number and alleles.
What's actually true: Meiosis separates the matching pairs, so each cell gets half the chromosomes, one of each pair, in its own mix of alleles.
- Mitosis copies a cell for growth and repair. Both daughter cells keep the full set and the same alleles.
- Meiosis copies the DNA once and divides twice. Meiosis I separates homologous chromosomes, the matching pairs, so a diploid cell, 2n, becomes haploid, n.
- Crossing over and the way each pair lines up independently give every cell its own mix of alleles, one per gene.
- Meiosis II splits the sister chromatids, leaving four haploid cells that differ from the parent. Fertilization later restores 2n.
On the exam: Mitosis copies. Meiosis halves the number and shuffles the alleles.