1. Warm-Up 12/4/12 1. What phases of mitosis are seen here? A B C
2. What are chromosomes made of?
3. What is the difference between somatic and germ cells?

2. Mitosis Review What is it: involves.. Nuclear Division
Where does it occur: different cells in body except for certain areas such as brain or nerve cells
Function: Grow and repair tissues
4 Parts: prophase, metaphase, anaphase, telophase
Produce: 2 identical cells w/ same number of chromosomes as parent cell in each new cell

3. Meiosis Overview
What is it: Nuclear divisions to reproduce an entire organism.
Where does it occur: Reproductive cells: Ovaries in females, Testes in males.
Function: To form gametes (egg & sperm)
8 Parts: Meiosis I – prophase I, metaphase I, anaphase I, telophase I
Meiosis II – prophase II, metaphase II, anaphase II, telophase II
Produces: 4 cells with HALF the number of chromosomes as parent cell in each new cell.

4. Sexual reproduction Fusion of two gametes to produce a single zygote.
Introduces greater genetic variation by allowing genetic recombination.
With exception of self-fertilizing organisms, like some plants, a zygote receives gametes from two different parents.

5. Terms you should know: Examples: humans have 46 chromosomes
Diploid (2n) - Normal amount of genetic material
Haploid (n) - 1/2 the genetic material.
Examples: humans have 46 chromosomes
Mitosis = 46 chromosomes in daughter cells (diploid)
Meiosis =23 chromosomes in each daughter cell (haploid)

6. Human egg = 23 chromosomes (Haploid)
Human sperm = 23 chromosomes (Haploid)
When egg is fertilized by sperm, the zygote now has 46 total chromosomes (diploid)
Q: After Mitosis, are the two new daughter cells genetically identical?
Q: After Meiosis, are the four new daughter cells genetically identical?

7. Interphase Sister chromatids During interphase, amount of DNA doubles
2 identical chromosomes 7

8. Meiosis I – Prophase I During prophase 1
homologous chromosomes stack up on top of each other.
Chromosomes often exchange parts and become recombined.
This process, called “Crossing Over,” increases genetic variety of resulting gametes!

9. Crossing over Crossing over produces recombinant chromosomes.
Meiosis KM

10. Chromosomes after crossing over
Meiosis KM

11. Meiosis I – Metaphase I
The chromosomes line-up in the middle of the cell. They’re arranged randomly (independent assortment)

12. Independent assortment
Meiosis KM

13. Meiosis I – Anaphase I
The chromosomes are separated, pulling homologous chromosome pairs to opposite ends of the cell.
Homologous Chromosomes

14. Telophase I & Cytokinesis
The cell separates!
Q: Are the two cells genetically identical?
Q: What has caused their differences?

15. Meiosis II – Prophase II & Metaphase II
Centrioles migrate to the poles again to prepare for a second division.
Sister chromatids line up in the middle. Again, randomly arranged along the equator. (Ind.Assrtmnt)
Sister Chromatids

16. Meiosis II – Anaphase II
Sister chromatids separates from each other.

17. Meiosis II – Telophase II & Cytokinesis
Nuclear envelope and nucleolus appear
4 Haploid cells are created
Notice the variety they all have!
Q: How can each of the haploid cells become diploid again?

18. Meiosis KM

19. Meiosis KM

20. Let’s See it all together

21. What happens when a fertilized gamete has too many or too few chromosomes?
Non-disjunction
When an abnormal separation occurs during meiosis I or meiosis II. The gametes will either have too few or too many chromosomes.

22. Conditions caused by non-disjunction
In humans, non-disjunction may lead to one of many serious medical conditions such as..
Down syndrome (trisomy 21)
Turner Syndrome (lack of X)
Klinefelter Syndrome (XXY)
Teenaged girls with Down syndrome

23. Just how much genetic variety?
23 chromosomes in haploid cells…
2n = 223 = _____ possible combination person?
8.3 mil.

24. Random Fertilization also increases variety
At least __________ combinations from Mom, and another ____________ from Dad …
_________ combinations for a diploid zygote!!!
8.3 million
8.3 million
70.3 trillion

25. What does this mean for us?
Chromosomes have genes that code for proteins that give us traits.
For example, hair is made of protein and depending on your genetics, your hair is made of a specific protein that causes your hair to be curly, wavy, or straight.
Some traits are expressed more strongly than others. These are called dominant traits. The weaker traits are said to be recessive.