1. Cell Division
&
Gamete Formation

2. Gamete Diploid Haploid Meiosis Homologous pair
OUTCOME QUESTION(S):
S1-1-05:
What role do gametes play in reproduction?
Vocabulary & Concepts 
Genetic Diversity
Gamete Diploid Haploid
Meiosis Homologous pair

3. + = Sexual Reproduction Two parents make ONE offspring
Offspring NEVER identical – genetic diversity
Requires the formation of specialized sex cells:
Gametes – cells used only for sexual reproduction
Male Gametes = Sperm
Female Gametes = Egg or Ovum
Since 2 gametes will be coming together each can only have to have ½ the chromosomes + =

4. + = Haploid sperm + Haploid egg = Diploid zygote MEIOSIS:
(23 chromosomes) (23 chromosomes) (46 chromosomes)
MEIOSIS:
Process of producing specialized haploid sex cells.
Having a FULL SET of chromosomes - diploid (2n) cell
Having a ½ SET of chromosomes – haploid (n) cell

5. MEIOSIS Producing cells with chromosome number half of the parent cell
Cells having pairs of homologous chromosomes - diploid (2n)
e.g. body (somatic) cells
Cells having one chromosome from each homologous pair - haploid (n)
e.g. gametes
Two nuclear divisions
Meiosis I and meiosis II
END RESULT:
***Four haploid cells are produced***

6. In a pair – one is from the mother and one from the father
Meiosis has two stages:
Reduction stage
Cut number of chromosomes in half – haploid
Separate homologous pairs
Homologous pair: chromosomes that pair up based on size and the genes that they contain.
In a pair – one is from the mother and one from the father

7. COMMON MISTAKE: Don’t confuse sister chromatids with homologous pairs.

8. See how the duplicated chromosomes (X) line up as pairs
Meiosis 1 – Reduction stage
See how the duplicated chromosomes (X) line up as pairs

9. Meiosis 1 – Reduction stage

10. Prophase I Chromosomes become visible Nuclear membrane disappears
Homologous chromosomes pair up
Crossing-over may occur between homologous chromosomes

11. Metaphase I
Homologous chromosomes lie up at the middle of the cell randomly

12. Anaphase I
The 2 members of each homologous pair of chromosomes separate from each other and move to opposite poles of the cell

13. Telophase I Nuclear membrane reforms Followed by cytoplasmic cleavage
Each cell has half the chromosome number as the parent cell

14. This you should recognize – just regular mitosis
Meiosis 2 – Division stage
This you should recognize – just regular mitosis
Centromere

15. Second Meiotic Division
Separation of chromatids of each chromosome
End Result
4 daughter cells with half of the chromosome number of the parent cells are formed

16. Prophase II
During prophase II the centrioles migrate to opposite poles and the spindle apparatus reforms.

17. Metaphase II
Metaphase II involves the chromosomes lining up along the metaphase plate to resume division. At this point the centromeres divide and separate the chromosomes.

18. Anaphase II
During anaphase II the sister chromatids are pulled to the opposite poles by the spindle fibers.

19. Telophase II
During telophase II the cell divides once again and undergoes reduction division which creates four haploid cells (n) from the previous two diploid (2n) cells through cytokinesis

20. End Result
***4 Genetically different Haploid (n) cells***

21. 2 identical diploid daughter cells
MITOSIS– in general
DIPLOID 2n
46 Chromosomes
DIPLOID 2n
2 identical diploid daughter cells

22. The way the chromosomes line up is the KEY difference
MEIOSIS– in general
DIPLOID 2n
46 Chromosomes
Reduction Stage
HAPLOID 1n
The way the chromosomes line up is the KEY difference
Division Stage
HAPLOID 1n
4 different gamete cells

23. What would happen if gametes are formed by mitosis?
Male (2n)
Female (2n)
Mitosis
Sperm (2n)
Egg (2n)
Fertilization
Zygote (4n)
Mitosis
Sperm/Egg (4n)
Fertilization
Zygote (8n)

24. The Significance of Meiosis
Leads to halving of chromosome number
Ensure that the diploid number of chromosomes can be restored after fertilization
Produce genetic variation by
Crossing-over between homologous chromosomes during Prophase I
Independent assortment of chromosomes during Metaphase I

25. Sources of Genetic Variation
Crossing-over between homologous chromosomes during meiosis
Independent assortment of chromosomes during meiosis
Random fusion of gametes during fertilization
Mutation

26. Comparison between Mitosis & Meiosis
Number of division
One
Two
No. of daughter cell produced by one parent cell
Two
Four
Type of cells produced
Somatic cells
Gametes
Chromosome number of daughter cells
Same as parent cell
Half of parent cells
Genetic make-up of daughter cells
Identical to parent cell
May be different from the parent cell

27. Comparison between Mitosis & Meiosis
Pairing of homologous chromosomes No
Yes
Crossing-over No
Yes
Occurrence
Growing tissues
Reproductive tissues
Role
Growth, repair, replacement of old tissues, asexual reproduction
Gamete formation for sexual reproduction

28. SPERMATOGENESIS – cell division process for making sperm
Gametes are made in organs called gonads.
Male gonad = testes
Notice one cell makes 4 male gametes - sperm
SPERMATOGENESIS – cell division process for making sperm

29. OOGENESIS – cell division process for making eggs
Female gonads = ovaries
Notice ONLY 1 ova (egg) receives enough cytoplasm to survive
OOGENESIS – cell division process for making eggs

30. One giant, health egg is produced to ensure success

31. Mitosis is used to grow from a single cell into a baby.
Sexual reproduction:
Sperm combines with the egg - fertilization
Gametes combine to form a zygote
After fertilization:
Mitosis is used to grow from a single cell into a baby.

33. Sexual Reproduction in Plants

34. Plants
Male gamete – pollen
(ON stamen)
Female gamete – eggs
(IN pistil)
Seeds are the zygotes
Ovary develops into fruit

35. PROS – Asexual Reproduction – CONS
No diversity in organisms
clones are vulnerable to disease/environment
Large number of offspring
made very quickly
Each offspring will be successful
clones are well adapted
Little possibility for evolution
clones are identical
Stay close together
colonies build if nutrients are present
Can lead to overcrowding
starvation if not enough nutrients
No need to waste energy
finding a sexual partner ?

36. PROS – Sexual Reproduction – CONS
High variation in offspring
less vulnerable to outside threats
More complex = More mistakes
increased mutations and errors
More variety = More evolution
superior offspring likely to carry on
No guarantees of success
unpredictable offspring
Two “parents”
better offspring care and protection
Takes time
Finding mate / fertilization ?
Takes energy
Making gametes / attracting mate

37. CAN YOU ANSWER THESE QUESTIONS? S1-1-05:
What role do gametes play in reproduction?
Vocabulary & Concepts 
Genetic Diversity
Gamete Diploid Haploid
Meiosis Homologous pair