Interphase.
Meiosis I.
- Generates the most diversity.
- Starts diploid.
- Prophase 1. DNA has already been replicated prior to Meiosis I. Homologous chromosomes pair (bivalents) to form synapses. Chromosomes condense.
- Bivalent. Has 2 chromosomes and 4 chromatids. A pair of homologous chromosomes.
- Homologous chromosomes. One maternal chromosome and one paternal chromosome.
- Synapses. Crossover “mutations” can occur when homologous chromosomes pair up.
- Synaptonemal complex. Protein that holds homologuess together.
- Prometaphase 1. Nuclear membrane disappears. One kinetochore per one chromosome (instead of per chromatid). Chromosomes attach to spindle fibers.
- Metaphase 1. Bivalents (2 chromosomes, 4 chromatids) align at metaphasic plate.
- Anaphase 1. Chiasmata separate. Chromosomes (each with 2 chromatids) move to opposite poles. Each daughter is now haploid (n).
- Telephase 1. Nuclear envelope may reform or it may just go into Meiosis 2.
- Chiasmata. The point where paired chromosomes remain in contact together during meiosis 1. X-shape area. Help keep homologues together after synaptonemal complex breaks down.
- Ends haploid.
Meiosis 2.
- There is no copying of DNA when going from Meiosis I to Meiosis II.
- “Meiosis for haploid cells”.
- Starts haploid.
- Meiosis 2 is shorter and simpler.
- Cells entering are haploid. They have one chromosome from each homologous pair. Each chromosome still has 2 sister chromatids.
- Prophase 2. Nuclear envelope (if it had reformed prior) breaks. Chromosome condense.
- Prometaphase 2. Spindle is fully formed. Each sister chromatid forms an individual kinetochore that attaches to spindle.
- Metaphase 2. Sister chromatids line up at metaphasic plate.
- Anaphase 2. Sister chromatids split up and move to opposite poles. Pulled apart by kinetochore microtubules.
- Telophase 2. Chromosomes decondense. Nuclear envelope reforms. Cytokinesis. Results with 4 haploid cells.
- Ends haploid.
Resources.
