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Meiosis & Sexual Reproduction

Learn about the processes of meiosis and sexual reproduction, as well as the advantages and disadvantages of asexual and sexual reproduction. Understand how meiosis and fertilization lead to genetic variation and the importance of these processes in the development of offspring.

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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?

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