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MEIOSIS

MEIOSIS. Making Sex Cells. Get the Lingo Down!!!. Somatic cell = body cell. Skin Nerve Blood. Human Chromosomes. How many chromosomes? 46 How many pairs of chromosomes? 23. Homologous Chromosomes.

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MEIOSIS

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  1. MEIOSIS Making Sex Cells

  2. Get the Lingo Down!!! • Somatic cell = body cell Skin Nerve Blood

  3. Human Chromosomes • How many chromosomes? • 46 • How many pairs of chromosomes? • 23

  4. Homologous Chromosomes • Two sister chromatids joined at the centromere From MOTHER plus • Two sister chromatids joined at the centromere From FATHER = • All Four Chromatids carrying genes controlling the same inherited characteristics

  5. Loci • The place on a chromosome where a specific gene is located • The plural is "loci," not "locuses." • EXAMPLE: gene for hair color • Gene for height

  6. Autosomes • Any chromosome that is not a sex chromosome • Humans - #1 through #22

  7. Sex Chromosomes • Female = XX • Male = XY • Chromosome #23 • Is this a male or female?

  8. Is this a male or female?

  9. Where do we get the pair of chromosomes? • One set from our father • One set from our mother

  10. Diploid number 2n 46 somatic cells Haploid number n 23 sex cells Human Cells

  11. Sex Cells • “Gametes” • EX: Egg and Sperm

  12. Are Gametes n or 2n? • N • Single set of chromosomes

  13. Are Gametes haploid or diploid? -Haploid = 23 -n 23 chromosomes egg 23 sperm

  14. Fertilization • Fusing of Egg and Sperm • Woo-Hoo! • What’s the Fertilized egg called? Zygote

  15. Where are the sex cells made? • Testes make sperm • Ovaries make eggs Only in reproductive organs

  16. What is the process… • In which sex cells are made? • MEIOSIS

  17. How many cells formed?Haploid or Diploid? 4 haploid 2 diploid

  18. MEIOSIS INTERPHASE • Yes, the chromosomes duplicate • Still chromatin, loose

  19. Meiosis I: Prophase I 90% of meiosis time

  20. Meiosis I: Prophase I Synapsis: formation of a tetrad (4 homologous chromosomes)

  21. Let’s Review: All DNA and Protein

  22. With Jonathan Edwards…whatever happened to him, anyway?

  23. Let’s See a Close-up: Crossing Over

  24. Chiasma • Sites of crossing over • Appear as X-shaped regions • Site where two homologous chromosomes are attached to each other

  25. Genetic Recombination • The production of gene combinations different from those carried by the original chromosomes • ADVANTAGE: increases diversity

  26. What else happens Prophase I? • What dissolves? • Nuclear Membrane and Nucleolus

  27. What else happens Prophase I? • What also forms? • spindles

  28. Meiosis I: Metaphase I Where are the tetrads lined up?Metaphase plate

  29. Meiosis I: Anaphase I Where are the sister chromatids going? Apart to the poles NOTE: the double strands

  30. Meiosis I: Telophase I Note the double strands at the poles Cytokinesis begins

  31. Interkinesis/Cytokinesis • Some cells will go into a temporary chromatin-forming interphase (like in humans) called interkinesis

  32. Interkinesis/Cytokinesis • Some will immediately go into Prophase II • NOT ALL CELLS DO THIS AT THE SAME TIME…BUT ALL WILL EVENTUALLY GO INTO PROPHASE II

  33. Interkinesis/Cytokinesis • (Different than mitosis interphase, however) • NO NEW DUPLICATION OF CHROMOSOMES… • FURTHER DIVISION OF THE CHROMOSOMES WILL OCCUR

  34. Meiosis II: Prophase II How many cells are there? 2 What is dissolving? Nuclear membrane What’s forming?New spindles

  35. Meiosis II: Metaphase II How many cells? 2 Where are the chromatids lined up?Metaphase (equatorial plate)

  36. Meiosis II: Anaphase II How many cells? 2 What are the single chromosomes doing?Moving to poles

  37. Meiosis II:Telophase II How many cells will result at the end? 4 Will the cells be haploid or diploid?Haploid

  38. Name the Phase (Meiosis I)

  39. Name the Phase (Meiosis II)

  40. Sperm MeiosisAll cells same size

  41. Sperm maturing in a seminiferous tubule

  42. Egg MeiosisOne large egg, 3 small polar bodies • “oogenesis”

  43. Follicle and egg

  44. MITOSIS 1 division (PMAT) Results in 2 daughter cells MEIOSIS 2 divisions (PMAT) I and (PMAT) II Results in 4 daughter cells Contrast

  45. MITOSIS Diploid offspring Makes somatic cells MEIOSIS Haploid offspring Makes sex cells Contrast

  46. MITOSIS Makes identical cells Same number of chromosomes MEIOSIS Makes similar cells Half the number of chromosomes Contrast

  47. Independent Assortment • This means that traits are transmitted to offspring independently of one another. • Independent Assortment Animation

  48. Independent Assortment • In other words, • RANDOM COMBINATION OF ALLELES APPEAR IN THE GAMETES

  49. How many possible combinations are there? • 2n • n = haploid number • 22 = ? • 8

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