1. Class Notes Sexual Reproduction Meiosis

2. Interphase (not part of mitosis)
Cell goes about its regular business
Copies are made of all the cells organelles
In the S stage of Interphase:
Each DNA Strand makes an exact copy of itself
The two identical strands are joined together by a centomere.
The joined strands are called sister chromatids

3. Prophase I Sister chromatids become visible in the nucleus
The nuclear membrane disappears
Sister chromatids form homologous pairs. Each pair is made of two sets of sister chromatids. The pairs swap genetic
material.
Homologous pair

4. Metaphase I
Spindle fibers pull the homologous pairs to the center of the cell. Each homologous pair is made of two sets of sister chromatids The pairs line up opposite each other.

5. Anaphase The cell elongates
The spindle fibers pull apart the homologous pairs and drag them to opposite sides of the cell.

6. Telophase I The spindle fibers disappear
The nuclear membrane forms around the chromatids
A cell membrane/ cell wall forms down the center of the cell
Two similar cells are created.

7. The cell makes copies of all its organelles.
Interphase
The cell makes copies of all its organelles.
The chromosomes
DO NOT replicate.

8. Meiosis II

9. Prophase II
Nuclear membrane breaks apart.

10. Metaphase II
Spindle fiber appear at each end of the cell and pull the sister chromatids to line up along the center.

11. Anaphase II
Spindle fibers pull apart the sister chromatids and pull the chromosomes toward each side of the cell.

12. Telophase II Spindle fibers disappear.
A nuclear membrane forms around the chromatids.

13. Cytokinesis The cytoplasm divides. 4 haploid cells are produced.
Each contains ½ the original
number of chromosome.
These are sex cells.(egg/sperm)

14. Meiosis Square Dance
Tune 2

15. Fertilization
A sperm and an egg cell each have ½ the number of chromosomes as the parent cell. When an egg and a sperm are combined, fertilization occurs. The homologous chromosomes from each parent combine together to create one new cell called a zygote. Once the egg is fertilized, the two haploid sex cells return to being one diploid cell.

16. Compare Mitosis and Meiosis

17. Comparing Meiosis and Mitosis
Characteristic
Mitosis
Meiosis
Chromosomes
Sister chromatids line up (2)
Homologous pairs of chromosomes line up (4)
Crossover occurs No
Yes
Number of Cell Divisions 1 2
Number of Daughter cells 4
Comparison to parent cell
Diploid
(same number of chromosomes as original)
Haploid
(1/2 the number of chromosomes as the original
Type of cells that result
All other cells
Sex cells (sperm/egg)

18. Vocabulary
Homologous pairs
Egg
Sperm
Zygote
Diploid
Haploid
Meiosis