1. Mitosis & Meiosis

2. Objectives
1- To understand the cell cycle: i.e steps of (Mitosis and Meiosis cell divisions) 2- Differentiate between Mitosis and Meiosis and their end results.

3. Mitosis: Is the somatic (body) cell division , for growth and repair.
Meiosis
-Is the division of gametes (sex cells)

4. Mitosis Mitosis animations:

5. Cell Cycle Stages 1- Interphase G1 Phase S Phase G2 Phase 2- M Phase
Cytokinesis

6. Interphase – Resting Stage
Cells carrying on normal activities
Chromosomes aren’t visible
Cell metabolism is occurring
Occurs before mitosis

7. G1 Phase Growth stage (synthesis of RNA and proteins)
Cell performs its specific functions
Cell increases in size
Cell prepares to copy its DNA
This is the longest phase of the cell cycle.

8. Synthesis (S) Phase Replication of DNA
Chromosomes are duplicated (each chromosome is formed of 2 chromatids formed of double helix of DNA).

11. G2 Phase Time between DNA synthesis & mitosis
It is a non-synthetic period

12. M Phase Cell growth & protein production stop
Cell’s energy used to make 2 daughter cells
Called mitosis or karyokinesis (nuclear division)

13. Stages of Mitosis Prophase Metaphase Anaphase Telophase
Mitosis animation:

14. Prophase DNA coils tightly & becomes visible as chromosomes
Nuclear membrane disappears
Nuceolus disappears
Centrioles migrate to poles
Spindles begin to form

15. Each Chromosome in prophase is formed of 2 identical chromatids joined at the centromere

16. Metaphase Spindle fibers from centrioles attach to each chromosome
Cell preparing to separate its chromosomes
Chromosomes move to the equatorial plane of the cell, become shorter, deeply stained and easily studied.

17. Anaphase Spindle fibres contract
The centromere of each chromosome divides longitudinally
The 2 chromatids separate apart and each moves to one pole of the cell

18. Telophase Separation of chromosomes completed
Nucleus & nucleolus reform
Chromosomes uncoil

19. Cytokinesis
Cytokinesis is the division of the cytoplasm of a parent cell
Occurs after chromosomes separate
Forms two, identical daughter cells

20. Meiosis It is formed of :
It is cell division occurring in the gonads (testes and ovaries) to produce gametes (sperms and ova).
It is formed of :
- Meiosis I (reduction division where a cell with 46 chromosomes --- 2 cells each has 23 chromosomes only.
- DNA replication takes place.
- Meiosis II which is the same as mitotic division but there is no DNA replication.
Meiosis animation:

24. Meiosis I Interphase
The chromosomes have replicated, and the chromatin begins to condense.

25. Meiosis I Prophase
-The chromosomes are completely condensed.
- In meiosis (unlike mitosis), the homologous chromosomes pair with one another

26. Meiosis I Metaphase
- Chromosome pairs are arranged in the equatorial plane.
- Spindles are formed, each attach to the centromere of ONE chromosome.
Cross over occurs in this step

27. Meiosis I Anaphase - spindles contract.
- Each SINGLE chromosome moves towards one pole of the cell.

28. Meiosis I Telophase - Formation of nuclear membrane.
- Division of cytoplasm.
- End result is formation of 2 daughter cells each one has ½ (haploid) number of chromosomes of the mother cell (46 = Diploid number).

29. Meiosis II There is no DNA replication.
The chromatids of each chromosome separate and each daughter cell divides.
At the end of Meiosis, there are four daughter cells from each parent cell. Each daughter cell has half the number of chromosomes of the parent (23 chromosomes in human).

31. IMPORTANCE OF MEIOSIS
1. Reduces the Diploid number of chromosome to Haploid.
2. Allows shuffling of maternal & paternal chromosomes between the gametes Segregation
3. Allows Crossing Over of chromosome segments:
It is the interchange of chromatid segments between paired homologus chromosomes which redistributes genetic material.
N.B. It enhances genetic diversity through cross over and segregation.

32. Mitosis Meiosis Occurs in somatic and germ cells - in germ cells
Single division divisions (meiosis I, II)
Chromosome no in daughter cell is (haploid no)
One chromatid of a chromosome goes Each chromosome of a
to each daughter cell homologous pair goes to
a daughter cell
No crossingover Crossing over

35. Thank You