2. Do Now Fill in the blank: Asexual reproduction is to mitosis as Sexual reproduction is to _________ Answer the following questions: What are homologous chromosomes? Why are you not identical to your parents or siblings?

3. 2006-2007 Meiosis & Sexual Reproduction

4. What if a complex multicellular organism (like us) wants to reproduce? – joining of egg + sperm Do we make egg & sperm by mitosis? ______

5. Some Vocab… n= chromosome number Haploid- refers to one set of chromosomes in the nucleus of a cell (n) Diploid- refers to two sets of chromosomes in the nucleus of a cell (2n)

6. Regents Biology Human female karyotype 46 chromosomes 23 pairs XX diploid = 2 copies 2n

7. Regents Biology 46 chromosomes 23 pairs XY Human male karyotype diploid = 2 copies 2n

8. Regents Biology gametes How do we make sperm & eggs?  Must reduce 46 chromosomes  23  must half the number of chromosomes  haploid 23 46 egg sperm 46 meiosis 46 fertilization 23 zygote

9. Regents Biology Meiosis makes sperm & eggs  46 chromosomes to 23 chromosomes  half the number of chromosomes 23 46 egg sperm 46 meiosis haploiddiploid

10. Regents Biology Paired chromosomes  Homologous chromosomes  both chromosomes of a pair carry “matching” genes  control same inherited characters  homologous = same information diploid 2n 2n = 4 homologous chromosomes double stranded homologous chromosomes eye color (brown?) eye color (blue?)

11. Regents Biology  Meiosis (Take out colored pencils- lets Draw!!!!)

12. Meiosis

13. Regents Biology Meiosis = reduction division  Meiosis  special cell division in sexually reproducing organisms  reduce number of chromosomes  2n  1n  diploid  haploid  half  makes gametes  sperm, eggs

14. Regents Biology Meiosis & mitosis  Meiosis to make gametes  sperm & egg  Mitosis to make copies of cells  growth  repair  development

15. Regents Biology mitosis zygote Putting it all together… 23 46 egg sperm 46 meiosis 46 23 fertilization mitosis & development meiosis  fertilization  mitosis + development 46 gametes

16. Regents Biology The value of meiosis  Consistency over time  meiosis keeps chromosome number same from generation to generation from Mom from Dad offspring DadMom

17. Regents Biology The value of meiosis  Change over time  meiosis introduces genetic variation  gametes of offspring do not have same genes as gametes from parents  new combinations of traits from Mom from Dad new gametes made by offspring offspring This is why You don’t look Exactly like Mom and Dad variation

18. Regents Biology How does this explain: family resemblance & differences! Why are the kids so similar to the parents but not exact?

21. Regents Biology Exit ticket What are the DISadvantages of asexual reproduction? What are the DISadvantages of sexual reproduction? What are the advantages of sexual reproduction? What are the advantages of asexual reproduction?