1. Mrs. Griffin

2. The birds and the bees…  Humans and most other animals reproduce sexually.  This means that two cells fuse to make a new “baby” organism.  These specialized cells are called gametes or sex cells  Sperm and egg cells are human gametes

3. Meiosis  What is it?  Who does it?  Where does it happen?  Why does it happen?  Why is a different process needed? Making sex cells (sperm and egg) All sexually reproducing organisms In males- testes In females- ovaries To all organisms to reproduce 1) Chromosome # needs to be cut in half 2) Creates genetic diversity

4. Meiosis MITOSIS Diploid zygote Diploid adult MEIOSIS Haploid gametes

5. Remember, humans have 23 pairs of chromosomes Pairs 1-22 are said to be Homologous chromosomes (they go together because they have same traits but are not identical) Gene for eye color Gene for hair color

6. Meiosis Meiosis is a special kind of cell division that halves the number of chromosomes in gametes. This insures that the correct number of chromosomes are passed on.

7. The goal is to make haploid sex cells First division Second division MotherFather Polar Bodies (not functional)

8. What would happen if two cells with 46 chromosomes fused? 46 chromosomes + 46 chromosomes 92 chromosomes….

9. Nondisjunction = chromosomes fail to “dis-join” or separate:  Trisomy=gamete with 3 of one type  Monosomy=gamete with 1 of one type  Tripoidy= zygote with three of one type

10. Down Syndrome= 3 of #21 Karyotype

12. Klinefelter’s = XXY

13. Some symptoms…  Delayed puberty  Loss of libido - reduced interest in sexual activity  Impotence  Reduced facial hair - reduction in need to shave  Tiredness  Reduced muscle power and stamina  Change in body shape - increased fat and breast development  Infertility  Osteoporosis - brittle bones resulting in fractures  Depression and sometimes dissocial behavior  Early heart disease

14. Turner’s Syndrome  XO sex chromosome  Instead of XX female or XY for male

16. Meiosis has two stages: Meiosis 1 and Meiosis 2  Meiosis 1: This is the stage where the chromosome number is halved  Includes 4 stages: Prophase 1 Metaphase 1 Anaphase 1 Telophase 1

17. Meiosis 1  Prophase 1 is similar in some ways to prophase in mitosis. Chromosomes condense Spindle fibers appear Nucleus and nucleolus disappear

18. UNLIKE in mitosis, homologous chromosomes line up next to each other during prophase This process is called synapsing Lined up homologues are called tetrads

19. When homologous chromosomes hang out so close to each other, they sometimes swap parts. This is called “crossing over”

20. Synapsis and Crossing Over in Action

21. Crossing over increases genetic diversity Why is this important for a species’ long-term survival?

22. During metaphase 1, tetrads line up on a metaphase plate

23. Then spindle fibers pull the homologous chromosomes apart in anaphase 1

24. In telophase 1, two daughter cells are formed. They are NOT identical! (Why?)

26. After Meiosis 1…  Homologous chromosomes have been separated.  Two non-identical daughter cells have been formed.  The chromosome number has been cut in half.

27. The big picture

28. Chromosomes are NOT duplicated again between Meiosis 1 and Meiosis 2 Why not?

29. Meiosis 2 is similar to mitosis  Two identical daughter cells are formed from each of the cells created in Meiosis 1  Includes 4 Stages: Prophase 2 Metaphase 2 Anaphase 2 Telophase 2

31. Meiosis II

32. Meiosis 2  Prophase 2: spindle reforms and chromosomes move toward the metaphase plate  Metaphase 2: sister chromatids lined up on the metaphase plate  Anaphase 2: sister chromatids are separated and pulled toward opposite poles of the cell  Telophase 2 and Cytokinesis: nuclei form at either pole and each cell is finally divided into two identical daughter cells

34. All together now…

36. Let’s compare mitosis with meiosis…