Notes:

Meiosis I

Prophase I Stages

Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis

Metaphase I

• Homologous pairs line up on a metaphase plate.
• Independent assortment: 50–50%
• Tetrads — pairs of homologous chromosomes.
• Euchromatin — mostly unpacked
• Heterochromatin — tightly packed
• Nucleosome → chromatin → chromosome (hetero, eu)

Recombination

• Recombination (crossing over) in Prophase I
  • Chiasmata — crossing over points

Cohesin

Keeps tetrads together until anaphase I

Shugosin

Protects CEN — center of tetrads.

Aneuploidy

• Aneuploidy due to non-disjunction
  • Meiosis I → all daughter cells aneuploidy
  • Meiosis II → half daughter cells have aneuploidy

Synapsis

The pairing or joining of homologous chromosomes.