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Meiosis

Meiosis. . Two Types of Diploid Cells In Sexual Organisms. Somatic. GERM. Body Cells Diploid Divide by mitosis to make exact copies In every tissue except reproductive tissue. “Germinating” (reproductive) cells Diploid

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Meiosis

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  1. Meiosis

  2. Two Types of Diploid Cells In Sexual Organisms Somatic GERM • Body Cells • Diploid • Divide by mitosis to make exact copies • In every tissue except reproductive tissue • “Germinating” (reproductive) cells • Diploid • (Most) Divide by meiosis to make gametes (sex cells) (sperm & ova) • In testes & ovaries

  3. Mitosis vs. Meiosis

  4. What is an “n”? Haploid (n) is the number of chromosomes in a gamete. Diploid (2n) – number of chromosomes in a somatic cell. You have one copy from the mother, and one copy from the Father.

  5. Meiosis is part of SEXUAL Reproduction (requiring 2 parents)

  6. In Meiosis: ONEdiploid, germ cell divides to become FOUR (4) daughter cells • (*circle*) … diploid / haploid • (*circle*) … somatic / gamete

  7. In order to go from diploid to haploid, Meiosis Involves Two Divisions Meiosis I Meiosis II • Splits homologous pairs of chromosomes • Splits sister chromatidsapart

  8. Time To Name The Phases • PROPHASE I • METAPHASE I • ANAPHASE I • TELOPHASE I • PROPHASE II • METAPHASE II • ANAPHASE II • TELOPHASE II

  9. Make 2 Tables TABLE I

  10. Make 2 Tables TABLE II

  11. PROPHASE I • Nuclear envelope disintegrates • Centrioles migrate, produce spindle fibers • Homologous chromosomes pair up • Homologous pairsCROSS OVER!

  12. PROPHASE I CROSSING OVER Occurs when homologous chromosomes exchange segments of genes

  13. METAPHASE I • Homologous pairs of chromosomes line up along metaphase plate

  14. ANAPHASE I • Homologous pairs pulled apart to opposite poles

  15. TELOPHASE I & CYTOKINESIS • Chromosomes (no longer homologous pairs!) prepare for meiosis II • Cytoplasm begins to split into first 2 (of 4) daughter cells

  16. TELOPHASE I & CYTOKINESIS NOTE: At the end of meiosis I, daughter cells are already Haploid! (because homologous pairs were separated)

  17. 2 haploid daughter cells then go through MEIOSIS II In Meiosis II, 2 haploid cells will separate sister chromatids to make 4 gametes!

  18. PROPHASE II • Centrioles migrate, produce spindle fibers Just like in mitosis!

  19. METAPHASE II • Chromosomes line up along metaphase plate Just like in mitosis!

  20. ANAPHASE II • Sister chromatids pulled apart to opposite poles Just like in mitosis!

  21. TELOPHASE II & CYTOKINESIS • Nuclear envelopes reform around 4 daughter cells • Cytoplasm splits to separate the 4 daughter cells • Each of the 4 daughter cells is a new gamete withgenetic information different from either parent!

  22. Is This Meiosis I or Meiosis II? Why?

  23. Is This Meiosis I or Meiosis II? Why?

  24. Meiosis II Meiosis I Check – Point: At what point do the cells become haploid?

  25. Mitosis v. Meiosis

  26. 200 to 400 million sperm per ejaculate! But what happens to the other 3 eggs? The largest ovum absorbs the others! Only one wins per cycle, usually

  27. Finally, Fertilization • Male and female gametes unite • Fusion of two haploid nuclei produces diploid nucleus • Egg + Sperm = Zygote(new life in one diploid cell)

  28. Meiosis and Sexual Reproduction Guarantee Variation and Diversity!

  29. Meiosis and Sexual Reproduction Guarantee Variation and Diversity! In Three Ways • Independent Assortment • Homologous Chromosomes separate randomly • Crossing Over • Homologous pairs exchange gene segments • Random Fertilization • Which sperm meets which egg? (game of chance)

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