Meiosis &             Sexual ReproductionAP Biology                         2007-2008
Cell division / Asexual reproduction    Mitosis            produce cells with same information              identical d...
Asexual reproduction     Single-celled eukaryotes          yeast (fungi)          Protists              Paramecium    ...
How about the rest of us?     What if a complex multicellular organism        (like us) wants to reproduce?            j...
Human female karyotype             46 chromosomes             23 pairsAP Biology
Human male karyotype             46 chromosomes             23 pairsAP Biology
Homologous chromosomes    Paired chromosomes            both chromosomes of a pair carry “matching” genes              ...
How do we make sperm & eggs?    Must reduce 46 chromosomes → 23            must reduce the number of chromosomes by half...
Meiosis: production of gametes    Alternating stages            chromosome number                                      h...
Sexual reproduction lifecycle                                                 2 copies                                   ...
Meiosis    Reduction Division         special cell division for          sexual reproduction         reduce 2n → 1n    ...
I.P.M.A.T.P.M.A.T  Overview of meiosis                          2n = 4   interphase 1         prophase 1   metaphase 1    ...
Double division   of meiosis             DNA replication  Repeat  I can’t                        Meiosis 1after you!hear m...
Preparing for meiosis    1st step of meiosis        Duplication of DNA                                                2n...
2n = 4   Meiosis 1                                  single                                             stranded    1st di...
Meiosis 2    2nd division of meiosis                                              1n = 2       separates sister          ...
Steps of meiosis    Meiosis 1            1st division of        interphase       meiosis separates        prophase 1   ...
Meiosis 1 & 2AP Biology
Trading pieces of DNA     Crossing over                          prophase 1             during Prophase 1, sister       ...
What are the   Crossing over                 advantages of                                crossing over in     3 steps   ...
Mitosis vs. MeiosisAP Biology
Mitosis vs. Meiosis     Mitosis                         Meiosis            1 division                   2 divisions   ...
Putting it all together… meiosis → fertilization → mitosis + development              gametes    46            23         ...
The value of sexual reproduction  Sexual reproduction introduces genetic variation        genetic recombination         ...
Variation from genetic recombination     Independent assortment of chromosomes          meiosis introduces genetic varia...
Variation from crossing over    Crossing over creates completely new      combinations of traits on each chromosome      ...
Variation from random fertilization     Sperm + Egg = ?            any 2 parents will produce a zygote with             ...
Sexual reproduction creates variability     Sexual reproduction allows us to maintain both     genetic similarity & differ...
Sperm productionEpididymis         Testis                                                 germ cell                       ...
Egg production     Oogenesis           eggs in ovaries halted            before Anaphase 1           Meiosis 1 complete...
Putting all                                                   your egg     Oogenesis                                 in on...
Differences across kingdoms      Not all organisms use haploid & diploid        stages in same way            which one ...
Any Questions??                    What are the                  DISadvantages of                 sexual reproduction?AP B...
Ghosts of Lectures Past                    (storage)AP Biology                             2007-2008
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55 ch12meiosis2008

  1. 1. Meiosis & Sexual ReproductionAP Biology 2007-2008
  2. 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. 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. 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. 5. Human female karyotype 46 chromosomes 23 pairsAP Biology
  6. 6. Human male karyotype 46 chromosomes 23 pairsAP Biology
  7. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 18. Meiosis 1 & 2AP Biology
  19. 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. 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. 21. Mitosis vs. MeiosisAP Biology
  22. 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. 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. 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. 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. 26. Variation from crossing over  Crossing over creates completely new combinations of traits on each chromosome  creates an infinite variety in gametesAP Biology
  27. 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. 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. 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. 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. 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. 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. 33. Any Questions?? What are the DISadvantages of sexual reproduction?AP Biology 2007-2008
  34. 34. Ghosts of Lectures Past (storage)AP Biology 2007-2008
  35. 35. AP Biology
  36. 36. AP Biology

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