25meiosis
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25meiosis

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  • Consider the greater variation with 23 pairs of chromosomes = mixing and matching
  • Consider the greater variation with 23 pairs of chromosomes = mixing and matching

25meiosis Presentation Transcript

  • 1. 2006-2007 Meiosis & Sexual Reproduction
  • 2. 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!
  • 3. Asexual reproduction
    • Single-celled eukaryotes
      • yeast
      • Paramecium
      • Amoeba
    • Simple multicellular eukaryotes
      • Hydra
        • budding
    What are the disadvantages of asexual reproduction? What are the 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?
    46 46 + 92 egg sperm zygote What if we did, then…. Doesn’t work! No!   
  • 5. Human female karyotype 46 chromosomes 23 pairs XX diploid = 2 copies 2n
  • 6. Human male karyotype 46 chromosomes 23 pairs XY diploid = 2 copies 2n
  • 7. How do we make sperm & eggs?
    • Must reduce 46 chromosomes  23
      • must half the number of chromosomes
      • haploid
    gametes egg sperm meiosis fertilization zygote 23 23 46 46 46 23 23
  • 8. Meiosis makes sperm & eggs
    • 46 chromosomes to 23 chromosomes
      • half the number of chromosomes
    egg sperm meiosis haploid diploid 23 23 46 46
  • 9. Paired chromosomes
    • Homologous chromosomes
      • both chromosomes of a pair carry “matching” genes
        • control same inherited characters
        • homo logous = same information
    diploid 2n 2n = 4 homologous chromosomes double stranded homologous chromosomes eye color (brown?) eye color (blue?)
  • 10. Meiosis 1 overview
    • 1st division of meiosis
    • 4 chromosomes
    • diploid
    • 2n
    • 2 chromosomes
    • haploid
    • 1n
    double stranded Copy DNA Line Up 1 Divide 1 gamete prophase 1 metaphase 1 telophase 1
  • 11.
    • 2nd division of meiosis
      • looks like mitosis
    Meiosis 2 overview
    • 2 chromosomes
    • haploid
    • 1n
    gametes Line Up 2 Bye Bye 2 telophase 1 metaphase 2 telophase 2 4
  • 12. Meiosis = reduction division
    • Meiosis
      • special cell division in sexually reproducing organisms
      • reduce number of chromosomes
        • 2n  1n
        • diploid  haploid
          • half
      • makes gametes
        • sperm, eggs
  • 13. Meiosis & mitosis
    • Meiosis to make gametes
      • sperm & egg
    • Mitosis to make copies of cells
      • growth
      • repair
      • development
  • 14. Sexual reproduction lifecycle
    • 1 copy
    • haploid
    • 1n
    • 2 copies
    • diploid
    • 2n
    • 1 copy
    • haploid
    • 1n
    meiosis fertilization We ’ re mixing things up here ! A good thing?
  • 15. Putting it all together…
    • meiosis  fertilization  mitosis + development
    mitosis zygote egg sperm meiosis fertilization mitosis & development gametes 23 23 46 46 46 23 23 46 46 46 46 46 46 46 46
  • 16. The value of meiosis 1
    • Consistency over time
      • meiosis keeps chromosome number same from generation to generation
    from Mom from Dad offspring Dad Mom
  • 17. 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
  • 18. 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
  • 19. Any Questions?? 2006-2007 What are the DIS advantages of asexual reproduction? What are the DIS advantages of sexual reproduction? What are the advantages of sexual reproduction? What are the advantages of asexual reproduction?