1. Thursday
Unit 6 Notes: Meiosis-1

2. (1) Big Ideas: Meiosis is used to make more sex cells.
Meiosis happens in stages like mitosis.
Meiosis divides twice.
Happens in Stages:
DNA condenses.
Homologous Pairs Line Up.
Genes are swapped.
Homologous Pairs separate.
End up with 2, 2n cells!

3. (2) Genetic Information:
Mitosis:
Start 2n  replicates to 4n during interphase
4n  final division ends w/2n
Meiosis:
4n  divides to 2n at end of Meiosis 1
2n  divides to 1n at end of Meiosis 2

4. (3) Meiosis-1 Stages: Prophase-1 Metaphase-1 Anaphase-1 Telophase-1
Cytokinesis  Not really part of Meiosis, but necessary!

5. The Parent Cell (Before the M Phase)
Nucleus
Un-Condensed DNA
Cell Membrane

6. (4) Prophase-1: DNA condenses into chromosomes.
Nuclear membrane dissolves.
Centrioles & Spindle Fibers prepare.

7. Dissolving Nuclear Membrane
*Alleles:
- A and a
- B and b
- D and d
Dissolving Nuclear Membrane B B D D d d A A
Centromere a a b b
Cell Membrane
Sister Chromatids (Replicated DNA)

8. (5) Metaphase-1:
Homologous Pairs of Sister Chromatids line up across the Metaphase Plate according to each other’s centromeres.
Crossing Over Occurs:
Adjacent segments of 2 chromosomes are swapped.
Same gene, different alleles.
Increases diversity + variation
Say What?!?:
Homologous Pairs  Pair of sister chromatids which carry the same GENES, but different ALLELES.

9. Sister Chromatids (Replicated DNA)
*Alleles:
- A and a
- B and b
- D and d
Tetrad of Homologous Pairs a a A A
Metaphase Plate d d D D
Centromere
Metaphase Plate B B b b
Metaphase Plate
Cell Membrane
Sister Chromatids (Replicated DNA)

10. Crossing Over *Alleles: - A and a - B and b - D and d A a A a D d D d

11. (6) Anaphase-1: Homologous Pairs of Sister Chromatids separated.
Each side receives each allele for a gene.

12. Cell Membrane A a a A D d D d b B b B
Separated Sister Chromatids

13. (7) Telophase-1: Homologous Pairs continue to separate.
End up with Sister Chromatids on each side.

14. Cell Membrane D d D d a A b B a A b B

15. (8) Cytokinesis: Cytoplasm pinches off.
Cell membrane closes around 2 daughter cells.

16. The Diploid (2N) Daughter Cells (After Meiosis-1)b B a A b B
The Diploid (2N) Daughter Cells (After Meiosis-1)