25meiosis
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This document provides an overview of meiosis and sexual reproduction. It explains that meiosis reduces the number of chromosomes from diploid to haploid to produce gametes like eggs and sperm. This is necessary for sexual reproduction in complex multicellular organisms. Meiosis introduces genetic variation between offspring and parents, allowing for evolution over time while also maintaining consistency in chromosome number across generations.
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25meiosis
- 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?
Editor's Notes
- Consider the greater variation with 23 pairs of chromosomes = mixing and matching
- Consider the greater variation with 23 pairs of chromosomes = mixing and matching