2. Cell Division Meiosis

3. Relationship Between Meiosis and Genetics Meiosis results in egg (females) and sperm (males) cells. When egg and sperm combine a new human is formed. The egg carries the genes from mom and the sperm carries the genes from dad You are a combination of genes from your mom and your dad! Your eye color, hair color etc. all depends on which egg cell and sperm cells combine!

4. Let Us Review Mitosis Cellular division involving replication and division of chromosomes (DNA). New cell contains complete set of chromosomes. (Two copies of genetic info.) Results in DIPLOID cells (chromosomes occur in pairs)

5. Diploid Cells Chromosomes after replication (ready for mitosis) Chromosomes in early interphase (actually chromatin) Both are Diploid Homologous Pairs

6. Diploid Cells cont. All body cells are diploid. Sex cells: egg and sperm are the only haploid cells

7. Sex Cells Germ Cells –Also know as Sex Cells Only contain one copy of genetic information Have one chromosome of each pair or half that of diploid cells. Haploid (N) state.

8. # of Chromosomes Total Chromosomes in a diploid cell # of homologous pairs in a diploid cell Total chromosomes in haploid cell HUMAN 46 CAT 36 23 18

9. Why is Haploid Important? If diploid cells are fertilized… + Chromosome will keep doubling!! 2N + 2N  4N

10. Why is Haploid Important? If haploid cells are fertilized… + Like all cells of the body!! N + N  2N

11. Sexual Reproduction Reproductive process in which haploid sex cells (gametes) fuse to produce a diploid fertilized egg (zygote) + EGG SPERM Fertilized Egg GAMETES (ZYGOTE)

12. MEIOSIS Cell division that reduces the number of chromosomes in half Occurs in sex cells (germ cells: Egg and Sperm) Two Divisions –MEIOSIS I –MEIOSIS II Meiosis I Meiosis II

13. Prophase I Chromosomes form Nuclear membrane and nucleolus disappear Synapsis – homologous chromosomes pair up Crossing Over – exchange of DNA creating genetic variability

14. Metaphase I Homologous chromosomes line up at the equator

15. Anaphase I / Telophase I ANAPHASE I: Homologous chromosomes separate and move to opposite poles Cells are still diploid TELOPHASE I: Cell membrane pinches in

16. Interphase????

17. Prophase II Cells are haploid. Cells get ready to divide again.

18. Metaphase II Chromosomes align at the equator Looks like mitosis

19. Anaphase II / Telophase II ANAPHASE II: Sister chromatids move to opposite poles TELOPHASE II: Cell membrane pinches in Nuclear membrane reappears.

20. Resulting Sex Cells Four HAPLOID sex cells are produced.

21. MEIOSIS