1. Meiosis (How It Happens)

2. What’s the big picture?
The purpose of meiosis is to produce GAMETES (sex cells-egg and sperm) that have only one set of chromosomes (haploid).

3. Phases of Meiosis Interphase Prophase I Metaphase I Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I
Meiosis II

4. Meiosis
These cells begin Meiosis II

5. Interphase
Interphase in meiosis occurs the same as in mitosis G1 S G2

6. Meiosis I (When Homologous Chromosomes Separate)

7. Prophase I Nuclear envelope disappears Spindle forms
Chromosomes condense
Homologous chromosomes pair up
Crossing over occurs

8. What is Crossing Over?
Homologous chromosomes join to form a tetrad and pieces of chromosomes are exchanged
This produces genetic recombination (gametes are NOT identical to parent cell)
Homologous chromosomes
Join to form a TETRAD

9. Crossing Over

10. Homologous Chromosomes during crossing over
height
height
Hair type
Hair type
Eye color
(blue)
Eye color
(brown)
Foot size
Foot size
earlobes
earlobes
Hair color
Hair color
MOM
DAD

11. Metaphase I
Homologous pairs of chromosomes line up along the equator of the cell

12. Anaphase I Homologous chromosomes separate and move to opposite sides.
Sister chromatids remain attached at their centromeres.

13. Telophase I Homologous chromosomes reach opposite ends
Nuclear envelopes reform
Spindle disappears
Chromosomes uncoil

14. Meiosis II (When Sister Chromatids Separate)

15. Prophase II Nuclear envelope disappears Chromosomes condense
Spindle forms

16. Metaphase II
Chromosomes line up
along equator of cell

17. Anaphase II Sister chromatids separate and move to opposite sides
Equator
Sister chromatids separate and move to opposite sides

18. Telophase II Nuclear envelopes reform. Chromosomes uncoil.
Spindle disappears.
Cytokinesis divides
the cells.

19. Results of Meiosis
4 haploid gametes (egg/sperm) that are each a different combination of the original cell

20. Meiosis: Two Part Cell Division
Sister
chromatids
separate
Meiosis I
Meiosis II
Homologous
Chromosomes
separate
Diploid
Haploid
Haploid

21. Comparison of Divisions
Mitosis
Meiosis
Number of divisions 1 2
Number of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent
Half of parent
Where
Somatic cells
Gametes
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction