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KEY CONCEPT Meiosis creates sex cells that are haploid

KEY CONCEPT Meiosis creates sex cells that are haploid. The Process of Meiosis. One parent cell produces 4 gametes /sex cells Sex cells have half the chromosome number (haploid) as the parent cell (diploid) Daughter cells are genetically different than parent cell.

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KEY CONCEPT Meiosis creates sex cells that are haploid

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  1. KEY CONCEPT Meiosis creates sex cells that are haploid

  2. The Process of Meiosis • One parent cell produces 4 gametes/sex cells • Sex cells have half the chromosome number (haploid) as the parent cell (diploid) • Daughter cells are genetically different than parent cell

  3. Meiosis is also known as Reduction Division because as the cell divides, its chromosome number is reduced

  4. from mom from dad child Too many! meiosis reduces genetic content Why must the genetic material be reduced? n (sperm) + n (egg) = 2n (zygote) Just right!

  5. Meiosis occurs in 2 Stages: • Meiosis I and Meiosis II

  6. In Meiosis I homologous chromosome pairs separate

  7. In Meiosis II sister chromatids separate

  8. Diploid2n Haploidn : Meiosis I (ANAPHASE I ) – Homologous Chromosome Pairs separate .

  9. Diploid2n Haploidn : Meiosis I (ANAPHASE I ) – Homologous Chromosome Pairs separate .

  10. Diploid2n Haploid n Haploid n : Meiosis I Meiosis II Homologous chromosomes separate Sister chromatids separate .

  11. WHAT’S THE DIFF???? • Homologous Chromosomes – * One inherited from each parent * Similar gene segments but NOT identical Sister Chromatids Sister Chromatids • Sister chromatids – * Made in Interphase “S” * Genetically identical

  12. Interphase I Cell carries out job Chromosomes stringy chromatin Chromosomes duplicated in “S” apart .

  13. Prophase I (Early) Chromosomes condense (coil) Nuclear membrane breaks apart Spindle fibers form .

  14. Prophase I Late Homologous chromosomes synapse and exchange DNA segments – crossing over Increases genetic diversity cause each chromosome now has genes from both parents mixed together

  15. Crossing Over – Increases genetic diversity This increases genetic diversity important for survival and evolution

  16. Metaphase I Homologous chromosomes line up side by side on the equator and attach to the same spindle fiber

  17. Anaphase I Homologous chromosomes separate and move to opposite poles. Each pole receives only 1 copy of each chromosome

  18. Telophase I and Cytokinesis Nuclear envelopes reforms Spindle fibers disappear Cytokinesis divides the cytoplasm into two cells

  19. End of Meiosis I • Results of Meiosis I • 2 Haploid Cells • No doubling of chromosomes occurs before Meiosis II

  20. Four Non-identical haploid daughter cells Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Meiosis II

  21. Prophase II Nuclear envelope breaks apart Spindle forms.

  22. Metaphase II Chromosomes line up on cell equator

  23. Anaphase II Sister chromatids separate and move to opposite poles.

  24. Telophase II and Cytokinesis Nuclear envelope forms Spindle fibers disappear Chromosomes unravel. Cytokinesis divides the cell’s cytoplasm into two cells

  25. End of Meiosis II 4 Cells with Haploid # Each cell is genetically unique

  26. Gametogenesis – Process of Haploid cells developing into mature gametes In males meiosis occurs in the testicles and forms sperm In females meiosis occurs in the ovaries and forms eggs

  27. SPERMATOGENESIS • Sperm get flagella and become swimmers. • Sperm mainly contribute DNA to an embryo.

  28. OOGENESIS Eggs contribute DNA, cytoplasm, and organelles to an embryo. Cytoplasm divides unevenly - the egg gets most of the contents; the other cells form 3polar bodies which can’t be fertilized.

  29. “Putting It All Together” - Fertilization

  30. What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction. Meiosis Video Link

  31. Meiosis Video Link #1 Meiosis Video Link #2 Meiosis Video Link#3

  32. Problems in Meiosis Nondisjunction – Failure of chromosomes to separate during Anaphase I or II Results in too many or too few chromosomes in offspring

  33. MeioticNon-disjunction (Trisomy 21: 75% meiosis 1) Trisomy Monosomy (lethal)

  34. Nondisjunction of Autosomes • Trisomy 21 – Down’s Syndrome • Trisomy 13 – Patau’s Syndrome

  35. Down’s Syndrome – Trisomy 21

  36. Patau Syndrome - Trisomy 13

  37. Nondisjunction - Sex Chromosomes • Turner’s Syndrome – X • Klinefelter’s Syndrome - XXY

  38. Meiosis differs from mitosis in significant ways. • Meiosis has two cell divisions while mitosis has one.

  39. Mitosis or Meiosis? • 2 diploid 4 haploid • Crossing over between nonsister chromatids • Reduction division • Increases genetic variability vs. clones • Meiosis 1 Homologous chrom separate • Meiosis 2 Sister chromatids separate

  40. Mitosis or Meiosis? • 2 diploid 4 haploid • Crossing over between nonsister chromatids • Reduction division • Increases genetic variability vs. clones • Meiosis 1 Homologous chrom separate • Meiosis 2 Sister chromatids separate

  41. Parental origin of meiotic error leading to aneuploidy

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