1. M EIOSIS

2. Recap of Asexual Reproduction
One parent
Genetically identical offspring
One organism can have many offspring

3. Sexual Reproduction
Involves sex cells joining to produce a zygote

4. Sexual reproduction
Requires two parents, a male and female.

5. Sexual reproduction
Both have sex organs

6. Sexual reproduction
The sex organs make sex cells (gametes)

7. Sexual Reproduction
Multicellular organisms that reproduce sexually have two types of cells:
Somatic Cells
Body cells, reproduce via cell division
Human somatic cells have 23 pairs of chromosomes (46 total)
Sex Cells (Gametes)
Have half the chromosomes of the parent cell (23 total)

8. Sexual reproduction
In male animals the sex cells are called sperm, made in sex organs called testes (testis is singular)

9. Sexual reproduction
In female animals the sex cells are called eggs, made in sex organs called ovaries.
An egg is released from the ovaries about every 28 days. This is called ovulation.

10. Sexual reproduction
During sexual reproduction the sperm and egg join together (fertilization)

11. External fertilization
In some animals fertilization takes place outside the body.

12. Chromosome Numbers
Individuals from the same species have the same number of chromosomes
Goldfish have 94 chromosomes
Fruit flies have 8 chromosomes
Humans have 46 chromosomes

13. Question
If sexual reproduction involves the fusing of genetic material from TWO individuals, then why doesn’t the resulting offspring contain twice the number of chromosomes?
The process that produces sex cells which have half the number of chromosomes as the parent = MEIOSIS

14. Meiosis
Meiosis ONLY happens in the cells that produce gametes (reproductive cells)
Meiosis sometimes called “reduction division”
Reduces the chromosome number by half
Example: fruit fly gametes have 4 chromosomes

15. Meiosis
Cells with half the chromosome number of the parent are called haploid (n)
Cells that have a complete set of chromosomes are called diploid (2n)

17. When do we produce sex cells?
Males produce sperm continuously after puberty.
Women produce all of their eggs when they are developing as a fetus.
They are produced and stored in the ovaries.
One egg completes its development once a month after puberty.

18. How do we produce new sex cells?
The cell replicates its genetic material.
The nucleus divides twice, producing 4 nuclei.
The cell divides into 4 new cells.
These then specialize to form sperm or ova.

19. Meiosis
The process by which a cell replicates its DNA, then undergoes 2 nuclear divisions to form haploid sex cells.

20. Meiosis Phases Two different phases Meiosis I Meiosis II
Very original…

21. Meiosis Phases
Meiosis I  Two daughter cells (a little different though compared to mitosis)
Meiosis II  Four daughter cells produced

23. What happens in meiosis
This cell contains one pair of chromosomes.
Our body cells contain 23 pairs.

24. What happens in meiosis?
The DNA in each chromosome replicates.
Each chromosome now has an identical copy attached.

25. What happens in meiosis?
Some chromosomes exchange different versions of their genes (eg blue eyes for brown eyes).

26. What happens in meiosis?
The nuclear membrane breaks down.
The pairs of each chromosomes are pulled apart.

27. What happens in meiosis?
The copies of each chromosome are then pulled apart.

28. What happens in meiosis?
4 new cells are made.
They contain half the original number of chromosomes.
These can now specialize to form sperm or eggs.

29. Questions How many chromosomes do human sperm and eggs contain?
Both contain 23 chromosomes.
Why is the chromosome number halved?
So that it can be restored at fertilization.

30. Project Representation of Meiosis Working in groups of 2/3
Diagrams, 3D models, play, song, dance, commercial, comic strip…