2. Meiosis is a process that reduces the amount of chromosomes in a cell to half the original amount Why would you want to reduce chromosomes to half? (check with your neighbor)

4. Egg = 23 Sperm = 23 Egg + Sperm = 46 in them. If meiosis reduces the chromosome number in half, how many chromosomes are in human sex cells?

5. Haploid (n)– a half set of chromosomes Diploid (2n) – a full set of chromosomes Somatic Cells = ALL body cells (blood, skin, etc) except gametes

6. Gamete Skin Cell Egg Somatic Cell Sperm Sex Cell Haploid or Diploid?

7. Homologous Chromosomes – chromosomes that have the same information Ex. Father/Paternal #11 chromosome Mother/Maternal #11 chromosome “Partner” up in Prophase 1

8. Crossing Over is the exchange of genetic material between homologous chromosomes Crossing Over acts as a source of genetic variation within a species

10. Stages of Meiosis Interphase — 1 time ONLY –Growth and replication of DNA PMATC— 2 times –Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

11. Diploid Cell—2 copies of each chromosome that replicated during Interphase

12. Crossing Over occurred during Prophase 1

13. Anaphase AWAY

14. Telophase I/Cytokinesis results in 2 Haploid Cells

15. Prophase II looks similar to Telophase I, but nuclear envelope is disappearing again

17. Anaphase Away—part II

18. Telophase II and Cytokineses results in 4 HAPLOID sex cells….or gametes….or egg….or sperm!

21. What’s different?

22. Egg (Ovum) is created in the Ovary

23. Sperm is created in the Testis

24. Diploid Numbers in other Organisms Name of OrganismDiploid NumberImage Adders-tongue Ophioglossum Ophioglossum reticulatum 1440 This fern has the highest known chromosome number of any life form Field Horsetail Equisetum arvense 216 Red viscacha rat Tympanoctomys barrerae 102 Highest number known in mammals, a tetraploid [3]. [3] Hedgehog 90

25. Diploid Numbers in other Organisms Name of OrganismDiploid NumberImage Turkey 80 Dogs, Coyotes, Dingos, and Wolves 78 Mule Horse/Donkey Cross 63 *Infertile Platypus 52 10 Sex Chromosomes Jack Jumper Ant2 for females, 1 for males

26. Karyotype – a “map” of chromosomes 2 Main Uses: Determine sex of the baby Screen for Chromosomal Abnormalities Ex. Down Syndrome

27. 22 pair of Autosomes + 1 pair of sex chromosomes = 23 Total pairs XX = Female XY = Male

30. Questions about Meiosis????

31. Quiz What are sex chromosomes called? How many chromosomes does a diploid cell have? Haploid? What is a karyotype used for?

32. Quiz What is the purpose of crossing over? What does meiosis in male gametes create?? What does meiosis female gametes create?