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Meiosis & Sexual Reproduction

Meiosis & Sexual Reproduction

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Meiosis & Sexual Reproduction

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  1. 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 seeingdouble!

  3. Asexual reproduction • Single-celled eukaryotes • yeast • Paramecium • Amoeba • Simple multicellular eukaryotes • Hydra • budding What are thedisadvantages ofasexual 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? No! What if we did, then….    + 46 92 46 egg sperm zygote Doesn’t work!

  5. 2n diploid = 2 copies Human female karyotype 46 chromosomes 23 pairs XX

  6. 2n diploid = 2 copies Human male karyotype 46 chromosomes 23 pairs XY

  7. 46 46 23 23 46 23 23 How do we make sperm & eggs? • Must reduce 46 chromosomes  23 • must half the number of chromosomes • haploid zygote egg meiosis fertilization sperm gametes

  8. 46 23 46 23 Meiosis makes sperm & eggs • 46 chromosomes to 23 chromosomes • half the number of chromosomes egg meiosis diploid haploid sperm

  9. Paired chromosomes • Homologous chromosomes • both chromosomes of a pair carry “matching” genes • control same inherited characters • homologous = sameinformation diploid2n 2n = 4 eye color (brown?) eye color (blue?) homologouschromosomes double strandedhomologous chromosomes

  10. doublestranded Meiosis 1 overview Divide 1 • 1st division of meiosis Copy DNA Line Up 1 prophase 1 metaphase 1 • 4 chromosomes • diploid • 2n telophase 1 • 2 chromosomes • haploid • 1n gamete

  11. 4 Bye Bye 2 Meiosis 2 overview • 2nd division of meiosis • looks like mitosis telophase 2 telophase 1 Line Up 2 metaphase 2 • 2 chromosomes • haploid • 1n gametes

  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 • 2 copies • diploid • 2n • 1 copy • haploid • 1n • 1 copy • haploid • 1n fertilization meiosis We’re mixing things up here! A good thing?

  15. 46 46 46 46 46 46 46 46 46 46 23 23 46 23 23 Putting it all together… meiosis  fertilization  mitosis + development gametes meiosis egg zygote mitosis &development fertilization mitosis sperm

  16. Dad Mom The value of meiosis 1 • Consistency over time • meiosis keeps chromosome number same from generation to generation from Mom offspring from Dad

  17. We’re mixing things up here! 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 variation from Dad from Mom offspring new gametes made by offspring

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

  19. What are theadvantages ofasexual reproduction? What are theDISadvantages ofasexual reproduction? Any Questions?? What are theadvantages ofsexual reproduction? What are theDISadvantages ofsexual reproduction?