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Meiosis

Meiosis. Square 1. Homologous Chromosomes. 1 chromosome from parent 1 chromosome from parent Tetrad. Square 2. Diploid. 2 sets (chromosomes) 2n Somatic cells Body cells ex.: liver, skin, etc. Human 2n = 46. Square 3. Haploid. 1 set (chromosomes) 1n Sex cells Sperm/Egg

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Meiosis

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  1. Meiosis

  2. Square 1 Homologous Chromosomes • 1 chromosome from parent • 1 chromosome from parent Tetrad

  3. Square 2 Diploid • 2 sets (chromosomes) • 2n • Somatic cells • Body cells • ex.: liver, skin, etc. • Human 2n = 46

  4. Square 3 Haploid • 1 set (chromosomes) • 1n • Sex cells • Sperm/Egg • Gamete • Human 1n = 23

  5. Square 4 WHY? • maintain chromosome # from gen. 2 gen. • 2n -> 1n • # of chromosomes cut in ½ by separating homologous chromosomes • Creates genetic variation • Used in sexual reproduction

  6. Do not write “Putting It All Together” Fertilization

  7. from mom from dad child too much! meiosis reduces genetic content Do not write Goal: reduce genetic material by half Why? n (mom) + n (dad) = 2n (offspring) Just right!

  8. Do not write Meiosis Overview • 2 rounds of cell division • Meiosis 1 called reduction division. (diploid cell becomes 2 haploid cells.) • Meiosis 2 divides 2 cells into 4 cells.

  9. Do not write Spindle fibers Nucleus Nuclear envelope Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (diploid) Telophase I (diploid) Meiosis I : the reduction division

  10. Square 5 MEIOSIS I: PROPHASE I Prophase I 2n: Homologs pair up Interphase

  11. Top 1/3 of squares 6/7 MEIOSIS I: PROPHASE I Crossing over • Portions of the homologous chromosomes exchange – more genetic variation

  12. Square 6 METAPHASE I • 2n: Homologs line up at Metaphase Plate • Law #1

  13. Square 7 ANAPHASE I • Homologs separate; move to opposite poles. • Sister chromatids remain attached

  14. Square 8 TELOPHASE I & CYTOKINESIS Cytokinesis divides cell in two (Reduction Division…2n 1n)

  15. Do not write Sister chromatids carry identical genetic information. Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Meiosis II Gene X

  16. Do not write Four Non-identical haploid daughter cells Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Meiosis II

  17. Square 9 PROPHASE II • Similar to mitosis… • 1n

  18. Square 10 METAPHASE II • Sister chromatids line up • 1n

  19. Square 11 ANAPHASE II • Sister chromatids separate • 1n • Law #2

  20. Square 12 TELOPHASE II & CYTOKINESIS • Four haploid cells • One copy of each gene

  21. Do not write Meiosis I (reduction division) Meiosis II Diploid Haploid Haploid Meiosis: cell division in two parts Sister chromatids separate Chromatids separate (equational division) 2n n n Result: one copy of each chromosome in a gamete.

  22. Square 13 VS.

  23. Square 14 VS.

  24. Square 15 LAW #1: INDEPENDENT ASSORTMENT • Homologous chromosomes do not affect how others sort • Gives even more genetic variation

  25. Square 16 LAW #2: SEGREGATION • Separation of alleles • Needed so gametes have only 1 set of each gene

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