2. How do we maintain 46 Chromosomes?
Produce gametes – half the number of chromosomes per cell
Humans have 23 chromosomes per gamete
Cell with ½ the number of regular chromosomes (n) is called haploid
Cell with all chromosome (2n) is called diploid

3. 6 Stages of Cell Division
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

4. Meiosis I Interphase – Chromosomes replicate Prophase I
homologous chromosomes pair
1 from mom, 1 from dad
Nuclear envelope breaks down, spindles form
Crossing over!

5. Meiosis I Metaphase I Anaphase I Telophase I
Homologous chromosomes line up at center
Anaphase I
Homologous pairs move to opposite sides of cell
Telophase I
Chromosomes uncoil
Cell divides

7. Meiosis II Prophase II - no DNA replication!!! Metaphase II
Chromosomes condense
Spindle fibers appear
Metaphase II
Chromosomes line up at center
Anaphase II
Chromosomes split and move to opposite sides
Telophase II
Nuclei form around chromosomes
Cells divide

9. Meiosis
Mitosis
Two cell divisions
Centrioles appear
Half the original chromosomes
Homologous Chromosomes pair up
Spindle fibers form
Cytokinesis
Four daughter cells
46 Chromosomes at end X X X X X X X X X X X

10. Meiosis
Mitosis
Chromosome Number:
Reduced by half (homologous pairs separate)
Remains the same
Pairing of Homologues:
Yes No
Function:
sexual reproduction
Cellular (asexual) Reproduction (cell division during which the cell nucleus divides); general growth and repair of the body
Number of Divisions:
2 nuclear and 2 cytoplasmic divisions
1 division of the nucleus and 1 Cytokinesis
Number of Cells produced: 4 2
Creates:
Sex cells only: Female egg cells or Male sperm cells
Makes everything other than sex cells (Somatic Cells)
Occurrence of Crossing Over:
Produces:
four haploid daughter cells
two diploid daughter cells
Genetically:
different
identical

12. Drawing Meiosis

13. 2. Metaphase I
1. Prophase I
3. Anaphase I
4. Telophase/Cytokinesis I

14. 3. Anaphase II
Prophase II
Cells from Meiosis I
2. Metaphase II
4. Telophase II
/Cytokinesis II

15. Mitosis/Meiosis Review
1. Number of Cells
Mitosis creates 2 identical cells
Meiosis creates 4 individual cells
2. Number of chromosomes
Mitosis creates cells with 46 chromosomes (2n – diploid)
Meiosis creates cells with 23 chromosomes (n – haploid)
3. Locations
Mitosis – somatic (“normal”) cells
Meiosis – gametes (sex) cells

16. What is crossing over? Agenda for Friday Dec 9th Finish meiosis notes
Meiosis internet lesson
Quiz Monday

17. Importance of Meiosis Genetic Variation
Random distribution of chromosomes occurring during meiosis
Different chromosomes are passed to offspring independently of each other

20. Sexual vs. Asexual Reproduction
Organisms inherit all chromosomes from single parent
Genetically identical
Chromosomes from 2 parents
Genetic variation
Why reproduce sexually?
Greater chance of beneficial mutations
Crossing over, random assortment

21. Check the correct box for each description
Meiosis
Mitosis
Two cell divisions
Creates gametes
Half the original chromosomes
Homologous Chromosomes pair up
Creates identical cells
Cytokinesis
Four daughter cells
Same number of chromosomes at end