1. Cell Division
Meiosis…page 263

2. Diploid A cell with two of each kind of chromosome 2n
Example: human 2n=46

3. Haploid A cell containing one of each kind of chromosome n
Example: human n=23

4. Why meiosis?
Mitosis produces cells with the same number and kinds of chromosomes
Bad for reproduction
Meiosis produces cells with half the number of chromosomes
Good for reproduction
Meiosis produces cells called gametes

5. Interphase
All the same steps as mitosis

6. Prophase I Same steps as mitosis
Homologous chromosomes line up with each other
Forms a tetrad
Portions of tetrad break off and switch places – crossing over
Crossing over makes new combinations of genes

7. Crossing Over…page 269

8. Prophase I

9. Metaphase I
Tetrads line up at equator

10. Anaphase I Homologous chromosomes are pulled apart
This reduces the number of chromosomes by half

11. Telophase I Same things happen as mitosis
Nucleus usually does not return

12. Meiosis II Chromosomes DO NOT replicate
This cycle is exactly like mitosis only with half the number of chromosomes
Produces 4 genetically different haploid cells

13. Meiosis

14. Nondisjunction Failure of chromosomes to split properly
End up with too many or too few chromosomes
Down Syndrome – have an extra #21 chromosome

15. Male vs. Female Gamete Formation