1. Meiosis

2. What is meiosis? A special type of cell division.
Only occurs in reproductive organs
Reduces the number of chromosomes in the nucleus -Reduction division

3. What does meiosis make? End result: - Gametes in animals
- Spores in plants

4. Body Cells A.K.A. somatic cells
Contain the total number of chromosomes in an organism
Diploid number (2n)
Humans have a diploid number of 46 chromosomes

5. Sex Cells
A.K.A. gametes
Contain half of the total number of chromosomes
Hap/oid number (n)
Humans have a haploid number of 23

6. What is the diploid number of corn? The haploid number?

7. How many PAIRS of chromosomes do humans have?

8. Is the chromosome number related to the complexity of the organism?

9. Example: Humans
Diploid =46 Haploid = 23
Female gamete = egg = n = 23 Male gamete = sperm = n = 23
Zygote (fertilized egg) = 2n = 46

10. 2n 2n
mitosis 2n
meiosis
meiosis
mitosis n
zygote 2n n
fertilisation

11. Chromosome Pairs Each diploid cell has two copies of each chromosome
One copy 'donated' by the haploid egg
One copy 'donated' by the haploid sperm

12. Chromosome Pairs genes
Tetrad:
- Two homologous chromosomes attached
Chromosome Pairs genes
Homologous Chromosomes
Tetrad
Matching chromosomes
Carry information for the same genes
Two homologous chromosomes attached

13. Divided into two parts: Meiosis I & Meiosis II
The Phases of Meiosis
Divided into two parts:
Meiosis I & Meiosis II

14. Homologous chromosomes form2n n
interphase
prophase I
metaphase I
anaphase I
telophase I
Homologous chromosomes align at equator and separate into chromosomes
DNA replication

15. Chromosomes align at equator and separate into sister chromatids
prophase II
metaphase II
anaphase II
telophase II

18. Gamete Formation Gametogenesis Development of gametes
Occurs in organs (gonads) of reproductive system
Ovaries
Testicles

19. Gamete Formation Oogenesis -In females - Produce eggs (ovum/ova)
Spermatogenesis. -In males
- Produce sperm

20. How Genetic Variation Occurs
Random Fertilization (not part of meiosis)
- picking a random mate
- determines which sperm fertilizes which egg Average number of sperm cells in the ejaculate of a healthy man: 200 and 500 million
an estimated 400,000 to 450,000 immature eggs residing in each ovary at puberty.
Any sperm can fertilize any egg.
The resulting zygote could contain anyone of more than 70 trillion possible combinations of chromosomes.

21. 2. Crossover (Recombination) Totally Random and mistakes can occur

22. 3. Random Line up During Metaphase I We have pairs of 23 so 223 = 8
3. Random Line up During Metaphase I We have pairs of 23 so 223 = 8.4 million combinations

23. 4. Random Seperation During Metaphase II and Anaphase II