1. Do Now What is the purpose of Mitosis?
If a cell that has 12 chromosomes in interphase goes through mitosis, how many chromosomes will be in each cell?
How is a baby made? (on a CELLULAR level…)

2. Objectives To list the steps of Meiosis.
To compare and contrast Meiosis and Mitosis.
To explain why Meiosis is necessary.

3. Meiosis Purpose: to make sex cells Gamete: sex cell Male gamete= sperm
Female gamete= egg (ovum)

4. Lets take a look at our cells
Somatic cells: Non-sex Cells
Our Somatic Cells contain 46 chromosomes
1 chromosome from Mom, and 1 from Dad. These are called homologous chromosomes.
Each gamete (sex cell) contains only 23 chromosomes!
Why are there are only 23 chromosomes in our sex cells but our somatic cells have 46?

5. Diploid vs. Haploid Diploid cell Haploid cell
Any cell with 2 homologous chromosomes
Abbreviated as 2n
Ex. Somatic Cells
Haploid cell
Any cell with a single chromosome set
Abbreviated as n
Ex. Gametes

6. How do we become a Diploid Zygote?
Haploid egg cell fuses with haploid sperm cell in a process called Fertilization.
Half from mom and half from dad make up our homologous chromosomes! (23 pairs)
Our cells then undergo mitosis to create us.
But how did our parents create the sex cells to produce us?

7. Meiosis Two divisions: Each are similar to mitosis
Meiosis I and Meiosis II
Each are similar to mitosis
Produces 4 daughter cells
Phases are still IPMAT, however there are two of each of the PMAT phases.

8. Meiosis: 2 Divisions Meiosis I: Meiosis II: Prophase 1 Metaphase 1
Anaphase 1
Telophase 1 and cytokinesis
Meiosis II:
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2 and cytokinesis

9. Crash Course Biology!

10. Prophase I
Pairing of homologous chromosomes occurs forming a tetrad. (synapsis)
Nuclear envelope breaks down.
Crossing over can occur- homologous chromosomes exchange genetic material.

11. Crossing Over Crossing over does NOT occur during mitosis.
Allows recombination of genes between chromosomes
How is crossing over related to genetic variation?

12. Metaphase I Chromosome centromeres attach to spindle fibers
Homologous chromosomes line up at the equator.

13. Anaphase I
Homologous chromosomes separate and move to opposite poles

14. Telophase I and Cytokinesis
The spindles break down.
Chromosomes uncoil and form two nuclei.
The cell divides, forms two new cells.

15. At the end of PMAT 1 …
You have two cells. They are NOT genetically identical because of the crossing over
Next, those two cells go through PMAT again.

16. Prophase II Chromosomes condense. Spindles form in each new cell
Spindle Fibers attach to chromosomes

17. Metaphase II
Chromosomes Line up at equator of each cell

18. Anaphase II
The sister chromatids are pulled apart at the centromere by spindle fibers
Move toward the opposite poles of the cell.

19. Telophase II and Cytokinesis
The chromosomes reach the poles, and the nuclear membrane and nuclei reform.
Spindle breaks down
Cytokinesis results in FOUR haploid cells
Each with n number of chromosomes.

20. At the end of meiosis We have 4 haploid offspring cells.
All Genetically DIFFERENT!!