1. Meiosis
Chapter 9

2. Asexual Reproduction Parent splits, fragments, or buds Advantage:
Mitosis in eukaryotes
Produces clones
Advantage:
Rapid and efficient
No need for a mate
Disadvantage:
Lack of genetic variability

3. Sexual Reproduction Gametes join to form zygote
Increases genetic variability
Offspring are different from either parent and each other
This may increase survival of some; may decrease chances for others
Somatic (body) cells have 2 sets of chromosomes – diploid (2n)
Gametes have 1 set – haploid (n)
Some plants are polyploid – 3 or more sets of chromosomes

4. Meiosis
Cell division to produce haploid gametes from diploid somatic cells
Also called ‘reduction division’
Consists of 2 divisions – meiosis I and meiosis II
Produces 4 cells

6. Meiosis I: Prophase I
Chromosomes condense and synapse to form a tetrad
Tetrad contains a homologous pair – one maternal homologue, one paternal homologue (each homologue is 2 sister chromatids)
Crossing-over occurs – DNA segments are exchanged
This genetic recombination increases variation

8. Meiosis I: Metaphase I
Homologous chromosomes are lined at the equatorial plate

9. Meiosis I: Anaphase I
Tetrads separate and homologous chromosomes (still with 2 sister chromatids connected) move to opposite poles
Separation is random between maternal and paternal homologues (independent assortment)

10. Meiosis I: Telophase I
Each nucleus now contains a haploid number of chromosomes even though each one is made of 2 sister chromatids
Cytokinesis divides the cell into 2
Interkinesis occurs – between meiosis I and meiosis II
DNA is NOT copied
Very brief

11. Meiosis II: Prophase II
Chromosomes condense but do not pair (no pairs exist)

12. Meiosis II: Metaphase II
Chromosomes line up at equatorial plate
Chromosomes are NOT in tetrads

13. Meiosis II: Anaphase II
Sister chromatids are separated and pulled to opposite poles

14. Meiosis II: Telophase II
Unduplicated single chromosomes
Nuclear envelope re-forms
Cytokinesis occurs

16. Gametogenesis Spermatogenesis Oogenesis
4 haploid sperm cells from each cell
Oogenesis
1 haploid ovum (egg) cell from each cell
There is an uneven division of cytoplasm during cytokinesis
Polar bodies generally disintegrate