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  1. BELL WORK • Get today’s note page from front table

  2. BELL WORK • Get out the notes packet over mitosis vs meiosis

  3. MITOSIS VS. MEIOSIS Mrs. Stewart Biology I Stewarts Creek High School

  4. Objectives: • Differentiate between the process of mitosis and meiosis • Demonstrate the movement of chromosomes throughout meiosis • Analyze how meiosis leads to genetic variation

  5. Face Partners: Raphael Michaelangelo

  6. Review • 2 ways for animals/cells to reproduce • Asexual reproduction • Mitosis • Binary fission • These are used to create daughter cells that are identical to parent cells • Sexual reproduction • This creates daughter cells that are genetically different from parent

  7. REVIEW: • Cell Cycle • Interphase • G1, S, and G2 • M-phase (mitosis) • P-M-A-T • Cytokinesis • Mitosis • Asexual reproduction • Produces 2 identical daughter cells • Daughter cells are diploid • Daughter cells are identical to parent/mother cell

  8. What differences can you see? • How many sets of chromosomes are in the cells that Meiosis produces? • How many cells does Meiosis produce? • How many divisions occur in Meiosis?

  9. Final Products: • Mitosis • 2 identical daughter cells • Somatic cells • Diploid • Meiosis • 4 genetically different daughter cells • Gametes • Haploid

  10. Mitosis vs. Meiosis Animation • Mitosis vs. Meiosis animation

  11. Mikey: Explain to Raph how meiosis differs from mitosis

  12. Phenomenon •

  13. Why are gametes haploid? Because two gametes fuse to create an offspring during sexual reproduction Sperm (23) + Egg (23) = Offspring (46)

  14. What happens in fertilization? • Fertilization of an egg • Zygote = the intial cell created from the fusion of a sperm and an egg

  15. Fertilization to Implantation

  16. Raph: summarize the process of fertilization for Mikey

  17. Bell Work: • Pick up the one note page up front • Copy down the process of binary fission in your class notebook

  18. Review: • How do both Meiosis AND Mitosis play a role in the creation and development of a new organism? Meiosis = creates the gametes used to fertilize/create the new organism Mitosis = how the new organism grows and develops past the zygote stage

  19. MEIOSIS: • The process of creating haploid gametes for sexual reproduction

  20. Vocabulary • Two categories for chromosomes: • Sex chromosomes (2 out of 46) • the 23rd pair • determine sex (gender) • Autosomes (44 out of 46) – all the rest

  21. KARYOTYPES • A picture taken from a microscope of all the chromosomes within a cell. • The chromosomes are then arranged in homologous pairs and given a set of numbers

  22. Karyotypes • Each homolog shares the same genes (the stripes) in the same location • NOTE: They do not have to have the same alleles

  23. Homologous Chromosomes • Homologous chromosomes (homologs) • The two copies of each autosome • They are a matching pair • Which means they have the same genes, in the same location. • Where did they come from? Why do you have two?

  24. Homologs come from mom and dad

  25. Matching socks = Homologs


  27. Mikey: Explain to Raph what a homologous chromosome pair is and where they came from.

  28. How did babies get one homologue from each parent? • Meiosis • Creates haploid sex cells • Each sex cell has 23 chromosomes that are randomly assorted • This occurs through two cell divisions

  29. Two Divisions: • Meiosis can reduce the amount of DNA within each daughter cell by dividing twice

  30. What are the steps? • Interphase • Phases of Meiosis I • Prophase I • Metaphase I • Anaphase I • Telophase I • Cytokinesis • Interkinesis • Phases of Meiosis II • Prophase II • Metaphase II • Anaphase II • Telophase II • Cytokinesis Division One Division Two

  31. Let’s see it in action! • Meiosis animation

  32. Interphase • DNA replicates • Makes the diploid (2n) cell now be (4n) • This process results in sister chromatids that will be attached by a centromere (X-shaped Chromosomes)

  33. This karyotype shows homologous chromosome pairs right after cell division has occurred.

  34. This karyotype shows homologs during prophase I after DNA replication has occurred Note how each chromosome has two chromatids that are EXACT copies of each other

  35. Prophase I • Homologous chromosomes find each other and pair up • This is called forming a tetrad • Crossing over occurs • Chromatids MAY exchange portions of DNA

  36. Bell Work • How does Prophase I contribute to genetic variation?

  37. Why is crossing over so important? • Crossing over exchanges pieces of the chromatids. This will cause a new combination of alleles • This leads to genetic variation • Because the chromatids that are passed to the offspring may have a different combination of alleles than the original chromatids • This means that if a gamete that contains the newly combined chromatid is used to fertilize a zygote, then the baby will have a different combination of traits than the parent. = Variation!

  38. Example: • A = Can roll tongue, and a = cannot roll tongue • B = Freckles and b = no freckles • It is now possible for baby to be able to roll tongue and have NO freckles, which was never possible for original chromosomes

  39. Prophase I • Homologues (homologous pairs of chromsomes) form Tetrads • Crossing Over occurs

  40. Raph: Explain to Mikey the difference between homologous chromosomes and a tetrad

  41. Mikey: Explain to Raph the process of crossing over and how that leads to genetic variation

  42. Metaphase I • Spindle fibers attach to the chromosomes • Tetrads line up in the middle of the cell Anaphase I • Fibers pull the homologous chromosomes toward • opposite ends of the cell Telophase I and Cytokinesis • Nuclear membranes form • Cell separates into two new cells

  43. Interkinesis • Resting period between Meiosis I and Meiosis II • DNA DOES NOT REPLICATE AGAIN HERE!

  44. Meiosis II • The daughter cells from Meiosis I divide again WITHOUT replicating their chromosomes • That leads to 4 gametes, each with half the number of chromosomes (haploid) as the original “mother” cell

  45. Prophase II Metaphase II • Spindle fibers form and move chromosomes to center • Spindle fibers attach to the chromosomes • chromosomes line up in the middle of the cell – similar to how they do in Mitosis Anaphase II • Fibers pull the sister chromatids toward • opposite ends of the cell Telophase II and Cytokinesis • Nuclear membranes form • Both cells separate – forming 4 new haploid cells