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55 ch12meiosis2008

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  • 1. Meiosis & Sexual ReproductionAP Biology 2007-2008
  • 2. Cell division / Asexual reproduction  Mitosis  produce cells with same information  identical daughter cells  exact copies  clones  same amount of DNA  same number of chromosomes  same genetic information Aaaargh! I’m seeingAP Biology double!
  • 3. Asexual reproduction  Single-celled eukaryotes  yeast (fungi)  Protists  Paramecium  Amoeba  Simple multicellular budding eukaryotes budding  Hydra What are the disadvantages of asexual reproduction? What are theAP Biology advantages?
  • 4. 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? No!What if we did, then…. 46 + 46 92 egg sperm zygoteAP Biology Doesn’t work!
  • 5. Human female karyotype 46 chromosomes 23 pairsAP Biology
  • 6. Human male karyotype 46 chromosomes 23 pairsAP Biology
  • 7. Homologous chromosomes  Paired chromosomes  both chromosomes of a pair carry “matching” genes  control same inherited characters  homologous = same information diploid single stranded homologous 2n chromosomes 2n = 4 double strandedAP Biology homologous chromosomes
  • 8. How do we make sperm & eggs?  Must reduce 46 chromosomes → 23  must reduce the number of chromosomes by half zygote 46 23 23 meiosis egg 46 23 46 23 fertilization spermAP Biology gametes
  • 9. Meiosis: production of gametes  Alternating stages  chromosome number haploid must be reduced  diploid → haploid  2n → n  humans: 46 → 23  meiosis reduces chromosome number  makes gametes  fertilization restores chromosome number  haploid → diploid  n → 2n diploidAP Biology
  • 10. Sexual reproduction lifecycle  2 copies  diploid  2n 1 copy  1 copy fertilization meiosis haploid  haploid In the next 1n generation…  1n We’re mixing things up here! A good thing? gametes gametesAP Biology
  • 11. Meiosis  Reduction Division  special cell division for sexual reproduction  reduce 2n → 1n  diploid → haploid  “two” → “half”  makes gametes  sperm, eggs Warning: meiosis evolved from mitosis, so stages & “machinery” are similar but the processes areAP radically different. Do not confuse the two! Biology
  • 12. I.P.M.A.T.P.M.A.T Overview of meiosis 2n = 4 interphase 1 prophase 1 metaphase 1 anaphase 1 n=2 n=2 prophase 2 metaphase 2 anaphase 2 telophase 2 n=2 telophaseAP Biology 1
  • 13. Double division of meiosis DNA replication Repeat I can’t Meiosis 1after you!hear me 1st division of meiosis separates homologous pairs Meiosis 2 2nd division of meiosis separatesAP Biology sister chromatids
  • 14. Preparing for meiosis  1st step of meiosis  Duplication of DNA 2n = 6  Why bother? single stranded  meiosis evolved after mitosis  convenient to use “machinery” of mitosis  DNA replicated in S phase of interphase of MEIOSIS (just like in mitosis) 2n = 6 doubleAP Biology M1 prophase stranded
  • 15. 2n = 4 Meiosis 1 single stranded  1st division of meiosis separates homologous pairs 2n = 4 double prophase 1 strandedsynapsis 2n = 4 metaphase 1 double stranded tetrad reduction telophase 1 1n = 2 I can’t Repeat doubleAP Biology after you! hear me stranded
  • 16. Meiosis 2  2nd division of meiosis 1n = 2 separates sister double chromatids stranded prophase 2 What does 1n = 2 this division look like? double metaphase 2 stranded 1n = 2 single stranded 4AP Biology telophase 2
  • 17. Steps of meiosis  Meiosis 1 1st division of  interphase meiosis separates  prophase 1 homologous pairs  metaphase 1 (2n → 1n)  anaphase 1 “reduction division”  telophase 1  Meiosis 2 2nd division of  prophase 2 meiosis separates  metaphase 2 sister chromatids  anaphase 2 (1n → 1n)  telophase 2 * just like mitosis *AP Biology
  • 18. Meiosis 1 & 2AP Biology
  • 19. Trading pieces of DNA  Crossing over prophase 1  during Prophase 1, sister chromatids intertwine  homologous pairs swap pieces of chromosome  DNA breaks & re-attachessynapsis tetrad AP Biology
  • 20. What are the Crossing over advantages of crossing over in  3 steps sexual reproduction?  cross over  breakage of DNA  re-fusing of DNA  New combinations of traitsAP Biology
  • 21. Mitosis vs. MeiosisAP Biology
  • 22. Mitosis vs. Meiosis  Mitosis  Meiosis  1 division  2 divisions  daughter cells  daughter cells genetically identical genetically different to parent cell from parent  produces 2 cells  produces 4 cells  2n → 2n  2n → 1n  produces cells for  produces gametes growth & repair  no crossing over  crossing overAP Biology
  • 23. Putting it all together… meiosis → fertilization → mitosis + development gametes 46 23 46 23 46 46 meiosis egg 46 46 46 23 46 46 46 46 23 zygote fertilization mitosis spermAP Biology development
  • 24. The value of sexual reproduction  Sexual reproduction introduces genetic variation  genetic recombination  independent assortment of chromosomes  random alignment of homologous chromosomes in Metaphase 1  crossing over  mixing of alleles across homologous chromosomes  random fertilization  which sperm fertilizes which egg?  Driving evolution  providing variation for natural selectionmetaphase1AP Biology
  • 25. Variation from genetic recombination  Independent assortment of chromosomes  meiosis introduces genetic variation  gametes of offspring do not have same combination of genes as gametes from parents  random assortment in humans produces 223 (8,388,608) different combinations in gametes new gametesfrom Mom AP Biology from Dad offspring made by offspring
  • 26. Variation from crossing over  Crossing over creates completely new combinations of traits on each chromosome  creates an infinite variety in gametesAP Biology
  • 27. Variation from random fertilization  Sperm + Egg = ?  any 2 parents will produce a zygote with over 70 trillion (223 x 223) possible diploid combinationsAP Biology
  • 28. Sexual reproduction creates variability Sexual reproduction allows us to maintain both genetic similarity & differences. Jonas BrothersAP BiologyBaldwin brothers Martin & Charlie Sheen, Emilio Estevez
  • 29. Sperm productionEpididymis Testis germ cell (diploid) Coiled seminiferous tubules primary spermatocyte (diploid) MEIOSIS I secondary spermatocytes (haploid) MEIOSIS II Vas deferens spermatids (haploid) spermatozoa Spermatogenesis  continuous & prolific process Cross-section of seminiferous tubule  each ejaculation = 100-600 million sperm AP Biology
  • 30. Egg production  Oogenesis  eggs in ovaries halted before Anaphase 1  Meiosis 1 completed during maturation  Meiosis 2 completed after fertilization unequal divisions  1 egg + 2 polar bodies Meiosis 1 completed during egg maturation ovulationWhat is the advantage ofthis development system? Meiosis 2 completed triggered by fertilization AP Biology
  • 31. Putting all your egg Oogenesis in one basket! primary follicles germinal cell (diploid) fallopian tube fertilization primary developing oocyte follicle (diploid) MEIOSIS I mature follicle with secondary secondary oocytefirst polar body oocyte (haploid) ruptured follicle (ovulation) MEIOSIS IIafter fertilization ovum (haploid) second corpus luteum polar body AP Biology
  • 32. Differences across kingdoms  Not all organisms use haploid & diploid stages in same way  which one is dominant (2n or n) differs  but still alternate between haploid & diploid  must for sexual reproductionAP Biology
  • 33. Any Questions?? What are the DISadvantages of sexual reproduction?AP Biology 2007-2008
  • 34. Ghosts of Lectures Past (storage)AP Biology 2007-2008
  • 35. AP Biology
  • 36. AP Biology