2. Regents Biology 2006-2007 Meiosis & Sexual Reproduction

3. Regents Biology Cell division / Asexual reproduction  Mitosis  produce cells with same information  identical daughter cells  exact copies  clones  same number of chromosomes  same genetic information Aaaargh! I ’ m seeing double!

4. Regents Biology Cell Division in Prokaryotes  Binary fission is the process of cell division in prokaryotes.

5. Regents Biology Asexual reproduction  Single-celled eukaryotes  yeast  Paramecium  Amoeba  Simple multicellular eukaryotes  Hydra  budding What are the disadvantages of asexual reproduction? What are the advantages?

6. Regents 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, then…. Doesn’t work! No! 

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

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

9. 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

10. Regents Biology Formation of Haploid Cells  Meiosis is a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell.  Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis.

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

12. 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?)

13. Regents Biology Meiosis I  Meiosis I includes prophase I, metaphase I, anaphase I, and telophase I.  Crossing-over, which is when portions of homologous chromosomes exchange genetics material, occurs during prophase I and results in genetic recombination.

14. Regents Biology Meiosis II  Meiosis II includes prophase II, metaphase II, anaphase II, and telophase II.  Four new haploid cells result.

15. Regents Biology Meiosis 1 overview  1st division of meiosis  4 chromosomes  diploid  2n  2 chromosomes  haploid  1n double stranded Copy DNALine Up 1 Divide 1 gamete prophase 1metaphase 1 telophase 1

16. Regents Biology  2nd division of meiosis  looks like mitosis Meiosis 2 overview  2 chromosomes  haploid  1n 4 gametes Line Up 2 Bye Bye 2 telophase 1 metaphase 2 telophase 2

17. Regents Biology Meiosis

18. 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

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

20. Regents Biology Development of Gametes  Spermatogenesis is the process by which sperm cells are produced.  Oogenesis is the process that produces mature egg cells.

21. Regents Biology Meiosis in Male & Female Animals

22. Regents Biology Sexual Reproduction  Sexual reproduction is the formation of offspring through meiosis and the union of a sperm and an egg.  Offspring produced by sexual reproduction are genetically different from the parents.

23. Regents Biology Sexual reproduction lifecycle  1 copy  haploid  1n  2 copies  diploid  2n  1 copy  haploid  1n meiosisfertilization We ’ re mixing things up here! A good thing?

24. 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

25. Regents Biology The value of meiosis 1  Consistency over time  meiosis keeps chromosome number same from generation to generation from Mom from Dad offspring DadMom

26. Regents Biology The value of meiosis 2  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 We ’ re mixing things up here! variation

27. Regents Biology How does this explain: family resemblance & differences! Why are the kids so similar to the parents but not exact? Martin & Charlie Sheen, Emilio Estevez Michael & Kirk Douglas Baldwin brothers

28. Regents Biology 2006-2007 Any Questions?? 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?