1. Meiosis and Mitosis

2. Basis of reproduction - Cell Division
Types of cell division
1. Duplicating - Mitosis
2. Reducing - Meiosis
Duplicating and reducing refer to the number of chromosomes in the cells after divisiion

3. Mitosis and Meiosis
Mitosis
Meiosis

4. Mitosis
- duplication of cells (at the end of the process - produce two cells with the same chromosome number (2N) as the parent cell)

5. Mitosis
Mitosis has 5 phases:
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase and Cytokinesis

6. centrioles
chromatin
What’s happening?
1. DNA has already been duplicated (chromatin)
2. Centrioles form

7. Mitotic spindle fibres
Prophase
Mitotic spindle fibres
sister chromatids
Condensing
chromatin
What’s happening?
1. Chromatin condenses and chromosomes become visible
2. Mitotic spindle fibres appear
3. Duplicated chromosomes appear as ‘sister chromatids’

8. Some terms about chromosome structure
Unduplicated
chromosome
Sister chromatids
Duplicated
chromosome
Centromere

9. Prometaphase Nuclear envelope Mitotic spindle kinetochore
What’s happening?
1. Nuclear envelop breaks down
2. Mitotic spindle invades nuclear area
3. Each sister chromatid develops a kinetochore at the centromere

10. Metaphase metaphase plate attached kinetochores What’s happening?
1. Chromosomes line up on ‘metaphase plate’
2. Kinetochores of each sister chromatid are attached to a spindle fibre

11. Spindle fibres contract
Anaphase
Spindle fibres contract
What’s happening?
1. Proteins holding sister chromatids together break down
2. Spindle fibres contract and pull sister chromatids apart

12. Telophase and Cytokinesis
Daughter nuclei
Cleavage furrow
Nuclear envelope
What’s happening?
1. Two daughter nuclei form
2. Nuclear envelope re-forms
3. Cleavage furrow forms, pinching the cell in two (cytokinesis)

13. Telophase & Cytokinesis
And to summarize ….. G2
interphase
Prophase
Prometaphase
Metaphase
Anaphase
Telophase & Cytokinesis
End up with two identical daughter cells

14. Meiosis
- reduction division of cells (at the end of the process - produce four cells each with the half chromosome number (N) as the parent cell)

15. Meiosis
Meiosis I
Meiosis II

16. (Purpose: To separate pairs of the same chromosome (homologous pairs))
Meiosis I
(Purpose: To separate pairs of the same chromosome (homologous pairs))
Meiosis II
Meiosis I

17. (Purpose: To separate pairs of the same chromosome (homologous pairs))
Meiosis I
(Purpose: To separate pairs of the same chromosome (homologous pairs))
Prophase 1
1. Chromosomes condense & homologous pairs line up side-by-side (synapsis)
2. Crossing over - homologous pairs exchange genetic material

18. (Purpose: To separate pairs of the same chromosome (homologous pairs))
Meiosis I
(Purpose: To separate pairs of the same chromosome (homologous pairs))
Metaphase 1
1. Chromosomes line up on metaphase plate. One pair on each side of the plate
2. Spindle fibres attach to kinetochores of each homologous chromosome

19. (Purpose: To separate pairs of the same chromosome (homologous pairs))
Meiosis I
(Purpose: To separate pairs of the same chromosome (homologous pairs))
Anaphase 1
1. Homologous chromosomes move to opposite poles of the cell

20. (Purpose: To separate pairs of the same chromosome (homologous pairs))
Meiosis I
(Purpose: To separate pairs of the same chromosome (homologous pairs))
Telophase 1 & cytokinesis
1. Cell divides into two cells each with half the number of chromosomes as the parent cell (haploid)

21. Meiosis II (- same process as mitosis but with 1/2 the chromosomes)
(Purpose: To separate sister chromatids)
Telophase & Cytokinesis
(Meiosis I)
Telophase & Cytokinesis
(Meiosis II)
Prophase
Metaphase
Anaphase

22. Comparison of Mitosis and Meiosis
Property Mitosis Meiosis
DNA replication During interphase During interphase
before mitosis before meiosis I
Number of divisions One Two
Synapsis of homologous Doesn’t occur During prophase I
chromosomes
Number of daughter cells
Number of chromosomes in each 2N (diploid) N (haploid)
daughter cell
Function of cells produced growth, maintenance gametes