Mitosis vs Meiosis
Mitosis and meiosis both start with copied chromosomes and both use chromosome-separation machinery. Their different jobs come from what pairs up and what gets separated.
| Mitosis | Meiosis | |
|---|---|---|
| Main job | growth, repair, cell replacement | make gametes |
| DNA replication | once | once |
| Cell divisions | one | two |
| Human starting cell | diploid (46 chromosomes) | diploid (46) |
| Products | 2 broadly genetically similar diploid cells | 4 genetically distinct haploid cells (23) |
| Homologs pair? | no | yes, in meiosis I |
| Crossing over? | normally no | yes, between homologs |
The conceptual trick
- Mitosis separates replicated copies. After DNA replication, sister chromatids are separated so each daughter cell receives a full genome.
- Meiosis I separates homologous chromosome pairs; meiosis II then separates sister chromatids. Maternal and paternal homologs pair in meiosis I, crossing over exchanges DNA between them, homologs separate, and the second division separates the copied chromatids.
That two-step design both halves chromosome number and reshuffles inheritance.