1. Bellringer
What are the differences between mitosis and meiosis?

2. Learning Targets
Explain the role of stem cells and the process of differentiation.
Explain the different purposes of mitosis and meiosis to produce haploid or diploid cells.
Compare and contrast the structure and function of autosomes and sex chromosomes.
Describe how meiosis occurs in the human body and how this process increases the genetic variation in gametes.
Compare and contrast asexual and sexual reproduction and how the processes impact diversity within a population.

3. Meiosis

4. 
Human Chromosomes
Human diploid somatic cells have 46 CHROMOSOMES – 2 COPIES OF 23 DIFFERENT CHROMOSOMES.

6. Human Chromosomes
Karyotype: systematized arrangement of chromosome pairs in descending order of size.

7. What is an “n”?  Haploid (n): Number of chromosomes in a gamete.
Diploid (2n):
Number of chromosomes in a somatic cell
One copy from mother, one copy from father.
Homologous pairs of chromosomes

9. Two Types of Diploid Cells In Sexual Organisms
Two Types of Diploid Cells In Sexual Organisms
Somatic
GERM
Body Cells
Diploid
Divide by mitosis to make exact copies
In every tissue except reproductive tissue
“Germinating” (reproductive) cells
Diploid
(Most) Divide by meiosis to make gametes (sex cells) (sperm & ova)
In testes & ovaries

10. Mitosis vs. Meiosis Asexual Reproduction Sexual Reproduction
Body cells (somatic)
Sex cells (gamete)
DNA replicates once
# cell divisions: 1
# cell divisions: 2
2 identical daughter cells
4 different daughter cells
Makes Diploids (2N)
Makes Haploids (1N)

11. Meiosis is part of SEXUAL Reproduction (requiring 2 parents)

12. In Meiosis: ONE diploid, germ cell divides to become FOUR
In Meiosis: ONE diploid, germ cell divides to become FOUR
(4) daughter cells
(*circle*) … diploid / haploid
(*circle*) … somatic / gamete

13. In order to go from diploid to haploid, Meiosis Involves Two Divisions
In order to go from diploid to haploid, Meiosis Involves Two Divisions
Meiosis I
Meiosis II
Splits homologous pairs of chromosomes
Splits sister chromatids apart

14. Time To Name The Phases PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II

16. PROPHASE I  Nuclear envelope disintegrates
Centrioles migrate, produce spindle fibers
Homologous chromosomes pair up
Homologous pairs CROSS OVER!

19. Exchange of segments of genes between homologous chromosomes
PROPHASE I
CROSSING OVER
Exchange of segments of genes between homologous chromosomes

21. 
METAPHASE I
Homologous pairs of chromosomes line up along metaphase plate

22. 
ANAPHASE I
Homologous pairs pulled apart to opposite poles

23. TELOPHASE I & CYTOKINESIS
TELOPHASE I & CYTOKINESIS
Chromosomes (no longer homologous pairs!) prepare for meiosis II
Cytoplasm begins to split into first 2 (of 4) daughter cells

24. TELOPHASE I & CYTOKINESIS
TELOPHASE I & CYTOKINESIS
NOTE:
At the end of meiosis I, daughter cells are already Haploid!
(because homologous pairs were separated)

25. 2 haploid daughter cells then go through MEIOSIS II
In Meiosis II, 2 haploid cells will separate sister chromatids to make 4 gametes!

26. 
PROPHASE II
Centrioles migrate, produce spindle fibers

28. 
METAPHASE II
Chromosomes line up along metaphase plate

29. 
ANAPHASE II
Sister chromatids pulled apart to opposite poles

30. TELOPHASE II & CYTOKINESIS
TELOPHASE II & CYTOKINESIS
Nuclear envelopes reform around 4 daughter cells
Cytoplasm splits to separate the 4 daughter cells
Each of the 4 daughter cells is a new gamete with genetic information different from either parent!

31. Is This Meiosis I or Meiosis II?
Why?

32. Is This Meiosis I or Meiosis II?
Why?

33. Meiosis I
Meiosis II
Check Point: When do the cells become haploid?

34. The largest ovum absorbs the others! Only one wins per cycle, usually
But what happens to the other 3 eggs?
The largest ovum absorbs the others!
Only one wins per cycle, usually

35. Finally, Fertilization
Male and female gametes unite
Fusion of two haploid nuclei produces diploid nucleus
Egg + Sperm = Zygote (new life in one diploid cell)

36. Meiosis and Sexual Reproduction Guarantee Variation and Diversity!
In Three Ways
Independent Assortment
Homologous Chromosomes separate randomly
Crossing Over
Homologous pairs exchange gene segments
Random Fertilization
Which sperm meets which egg? (game of chance)

38. Cell Differentiation
Humans are conceived when a sperm and egg unite, which forms a single-celled zygote.
Zygotes are unspecialized.
When born, humans have over 260 specialized cell types! This happens because of cell differentiation!

39. Cell Differentiation
Cells specialize by differentiating into different cell types.
Cells will turn off parts of DNA they don’t need and use only the parts of the DNA they need to become a specialized cell.

41. Stem Cells
Unspecialized cells that can become ANY type of cell in the body.
Stem cells found in every organ of the body.