1. Meiosis

2. Chromosomes
Key feature of a chromosome: centromere (where spindle attaches)
Chromosomes come in 2 forms, depending on the stage of the cell cycle. The monad form consists of a single chromatid.The dyad form consists of 2 identical chromatids (sister chromatids) attached together at the centromere.
Chromosomes are in the monad and dyad forms at different times during the cell cycle.
The dyad form is the result of DNA replication: a single piece of DNA (the monad chromosome) replicated to form 2 identical DNA molecules (the 2 sister chromatids of the dyad chromosome).

4. More Chromosomes
Diploid organisms have 2 copies of each chromosome, one from each parent. The two members of a pair of chromosomes are called homologues.
Each species has a characteristic number of chromosomes, its haploid number n. Humans have n=23, that is, we have 23 pairs of chromosomes. Drosophila have n=4, 4 pairs of chromosomes.

5. Human Karyotype

7. Meiosis Purpose – produce gametes (sex cells) for reproduction.
Location – gonads / sex organs only
Meiosis is the special cell division that converts diploid body cells into the haploid gametes. Only occurs in specialized cells.
Takes 2 divisions, Meiosis1 and M2
In humans, cells start with 46 chromosomes (23 pairs) in dyad state. After M1, there are 2 cells with 23 dyad chromosomes each. After M2 there are 4 cells with 23 monad chromosomes each.

8. Summary of Main Events Monad chromosomes duplicate to form dyad
Homologous chromosomes fuse to form tetrad/homologous pairs
Crossing over between non-sister chromatids
Independent assortment during anaphase I ~forms 2 different cells
Sister chromatids separate during anaphase II ~forms 4 different cells

9. Comparing Mitosis / Meiosis

11. Genetic Recombination
Purpose: to create chromosomes that are a new combination of paternal and maternal material
Genetic variation is important to the survival of every species.

13. Nice "current event" tie in to mitosis/stem cells/etc… http://video