2. AP Biology 2007-2008 Meiosis

3. AP Biology Cell Division / MITOSIS  Mitosis produce cells with same information  exact copies  clones Aaaargh! I ’ m seeing double!

4. AP Biology Asexual Reproduction  Single-celled eukaryotes  yeast “FungusAmongUs”  Protists  Paramecium  Amoeba  Simple multicellular eukaryotes  Hydra budding

5. AP Biology How about the rest of us?  What if a complex multicellular organism (like us) wants to reproduce?  joining of egg + sperm  Do we make egg & sperm by mitosis? 46 + 92 eggspermzygote What if we did…. Doesn’t work! No!

6. AP Biology So what do we do?  Must reduce 46 chromosomes  23  must reduce the number of chromosomes by half 23 46 egg sperm 46 meiosis 46 fertilization 23 gametes zygote

7. AP Biology Starts with Homologous Chromosomes  Paired chromosomes that each carry “matching” genes  homologous = same information diploid 2n 2n = 4 single stranded homologous chromosomes double stranded homologous chromosomes

8. AP Biology How many chromosomes do we have?

9. AP Biology What do we call our chromosomes? Pairs 1-22 are called autosomes Pair #23 are our sex chromosomes

10. AP Biology We organize chromosomes into a karyotype

11. AP Biology Human female karyotype 46 chromosomes 23 pairs

12. AP Biology Human male karyotype 46 chromosomes 23 pairs

13. AP Biology Well hello Meiosis (reduction division)  Meiosis - special cell division only in sexually reproducing organisms  reduces number of chromosomes  Humans = 46  23  2n  1n (where n = # of chromosomes from parents)  diploid  haploid  Meiosis makes gametes  sperm & egg cells What are gametes?

14. AP Biology Meiosis: production of gametes  Alternating stages of chromosome number  Only have 2 types of cells  Gametes – sperm & egg  Somatic Cells – everything else haploid diploid

15. AP Biology Overview of Meiosis I.P.M.A.T.P.M.A.T interphase 1prophase 1metaphase 1anaphase 1 telophase 1 prophase 2 metaphase 2anaphase 2telophase 2 2n = 4 n = 2

16. AP Biology 2n = 6 double stranded 2n = 6 single stranded Preparing for Meiosis  1st step:  Duplication of DNA  DNA replicated in S phase of interphase of MEIOSIS (just like in mitosis)

17. AP Biology Meiosis 1 Goal 2n = 4 double stranded prophase 1  1st division of meiosis separates homologous pairs tetrad synapsis 1n = 2 double stranded telophase 1 2n = 4 double stranded metaphase 1 “Reduction Division” 2n = 4 single stranded

18. AP Biology Meiosis 2 Goal 1n = 2 double stranded metaphase 2 1n = 2 single stranded telophase 2 prophase 2 1n = 2 double stranded  2nd division of meiosis separates sister chromatids 4

19. AP Biology Mitosis vs. Meiosis

20. AP Biology But how do we explain family resemblance & differences! Martin & Charlie Sheen Michael & Kirk Douglas Baldwin brothers Kardashians Have to wait till next class

21. AP Biology mitosis zygote Putting it all together… 23 46 egg sperm 46 meiosis 46 23 fertilization meiosis  fertilization  mitosis + development 46 gametes Any questions? No, then lets do like a baby and head out! sex cells