1. MEIOSIS
Making gametes…

2. Recall… CHARACTERISTICS OF LIVING THINGS ALL LIVING THINGS REPRODUCE

3. MITOSIS CREATES DIPLOID BODY CELLS
Makes 2 cells genetically identical to parent cell & to each other
Used by organisms to: increase size of organism, repair injuries, replace worn out cells

4. MEIOSIS CREATES HAPLOID SEX CELLS
Makes 4 cells genetically different from parent cell & from each other
Used for sexual reproduction

5. Stages of Meiosis

6. Meiosis

7. Meiosis takes place in two series of steps
Meiosis I I, P, M, A, T +
Meiosis II P, M, A, T
Which means…no DNA replication before meiosis II
No second “I”

8. Interphase I
DNA replicates creating homologous chromosomes

9. HOMOLOGOUS CHROMOSOMES
SAME SIZE
SAME SHAPE
CARRY GENES for the SAME TRAITS

10. PROPHASE I
Homologous chromosomes pair up to form a TETRAD (4 chromatids)
Images modified from:

11. Homologous pairs exchange DNA
2. CROSSING OVER
Homologous pairs exchange DNA
After crossing over, chromatid arms are NOT IDENTICAL anymore

12. Metaphase I
Tetrads line up in the middle

13. Anaphase I- Tetrads pull apart to opposite ends of the cell.

14. Telophase I- Cell separates into two new cells

15. No Interphase II which means chromosomes are NOT copied again.
Meiosis II
No Interphase II which means chromosomes are NOT copied again.

16. Prophase II ~ TWO cells begin meiosis II

17. Metaphase II chromosomes line up in the middle of the cell

18. Anaphase II -chromosomes are pulled to opposite ends of the cell

19. Telophase II / Cytokinesis ~ The two cells divide to form 4 genetically different cells (gametes)

20. End Result of Meiosis Four new cells
Half # chromosomes as parent cell - haploid (n)
Making of gametes

21. End Result of Mitosis TWO new cells
SAME # chromosomes as parent cell - diploid (2n)
Repair or Replace cells

22. Meiosis Video