1. Meiosis
Creating Cells for Sexual Reproduction

2. Meiosis Takes place in Gametes(sex cells)
Produces a haploid cell (represented by N)
People have 46 Chromosome or 23 pairs (2N)
When an egg joins a sperm the count must stay at 46 to remain human
egg can only have 23
sperm can only have 23
How does this happen?

3. Definitions
Diploid Cells- (2N)cells that have pairs of chromosomes. There are 2 of each chromosome in diploid cells.
Haploid Cells- (N)cells that have only one of each chromosome. Haploid cells are used for sexual reproduction.
Somatic Cells – body cells that are Diploid.
Gametes or germ cells – sex cells that are Haploid.

4. During Meiosis gamete (sex) cells undergo a “double division”, called Meiosis I and Meiosis II.
This maintains the DNA, but reducing the chromosomal count to 23. + =
Sperm (23) Egg (23) = Fertilized Cell (46)
Haploid Cells (N)
Haploid Cells (N)
Diploid Cells (2N)

5. Meiosis I

6. Prophase I Chromosomes already copied Centrioles separate
Nuclear membrane breaks down
Crossing over occurs here

7. Crossing Over Synapsis- Homologous Pairs line up = Tetrad
chromatids of homologous pair may twist around each other and break off and attach to the other homologous pair = Crossing Over
Results in exchange of genetic material between maternal and paternal chromosomes = genetic recombination

8. Metaphase I
Chromosome pairs line up at equator

9. Anaphase I
Chromosome pairs split
Sister chromatids stay connected

10. Telophase I Cell starts to divide in two
Nuclear membranes start to form again

11. Meiosis II

12. Prophase II Chromosomes do not replicate again
Cells have one set of sister chromatids
Nuclear membrane breaks down
Centrioles separate

13. Metaphase II
Sister chromatids line up at equator

14. Anaphase II
Sister chromatids divide

15. Telophase II Cells start to split in two
Each cell has one set of chromosomes—it is now haploid
4 cells form

16. Original Gamete Metaphase Anaphase Telophase Cytokinesis
2 Daughter Cells Metaphase 2 Anaphase 2 Telophase 2 Cytokinesis – 4 Gametes

17. OOGENESIS – Meiosis in females
SPERMATOGENESIS
- Meiosis in Males

18. Meiosis ensures that all living organisms maintain both Genetic Diversity and Genetic Integrity

19. Cell Division in Prokaryotes
Lack a nucleus
Have a single chromosome
Reproduce by binary fission
Include bacteria

20. Steps in Binary Fission
Cells increase cell mass
the single, circular bacterial chromosome is replicated
Each cell divides into 2 daughter cells