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meiosis powerpoint presentation

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meiosis powerpoint presentation

  1. 1. GRADE 12: MEIOSIS
  2. 2. © 2012 Pearson Education, Inc.
  3. 3. Why do gonosome undergo meiosis? Why do meiosis? Meiosis is “REDUCTION DIVISION”so Reduces chromosome number, parent cell is 2n while daughter cells are n.
  4. 4. Haploid gametes (n = 23) A life cycle n Egg cell n Sperm cell Meiosis Ovary Fertilization Testis Diploid zygote (2n = 46) 2n Key Multicellular diploid adults (2n = 46) Mitosis Haploid stage (n) Diploid stage (2n)
  5. 5. © 2012 Pearson Education, Inc.
  6. 6. QUIZ TIME… 1. In streptomycin fungus n = 11. What is the diploid number for this species? 2. If a horse egg has 98 chromosomes how many does a horse egg cell have? 3. If n = 16 for goldfish how many chromosome in a fin cell? 4. If 2n = 108 for black spruce trees then what is the haploid number? 2n = 14 for this species. Fill in the chromosome numbers for A each cell. B C What is process A, B, and C?
  7. 7. Sex Chromosomes XX chromosome - female XY chromosome - male
  8. 8. Meiosis I (four phases) • Cell division that reduces the chromosome number by one-half. • four phases: phases a. prophase I b. metaphase I c. anaphase I d. telophase I
  9. 9. Interphase I
  10. 10. Interphase I chromatin nuclear membrane cell membrane nucleolus
  11. 11. MEIOSIS I : prophase i
  12. 12. MEIOSIS I : prophase i © 2012 Pearson Education, Inc.
  13. 13. Metaphase I • Shortest phase • Tetrads align on the metaphase plate. plate • INDEPENDENT ASSORTMENT OCCURS: 1. Orientation of homologous pair to poles is random. 2. Variation 3. Formula: 2n Example: 2n = 4 then n = 2 thus 22 = 4 combinations
  14. 14. Metaphase I OR metaphase plate metaphase plate
  15. 15. Anaphase I • Homologous chromosomes separate and move towards the poles. • Sister chromatids remain attached at their centromeres. centromeres
  16. 16. Anaphase I
  17. 17. Meiosis i: telophase i © 2012 Pearson Education, Inc.
  18. 18. Meiosis ii © 2012 Pearson Education, Inc.
  19. 19. Meiosis ii: prophase II © 2012 Pearson Education, Inc.
  20. 20. Prophase II • same as prophase in mitosis
  21. 21. Metaphase II metaphase plate metaphase plate
  22. 22. Anaphase II
  23. 23. Telophase II
  24. 24. Crossing over © 2012 Pearson Education, Inc.
  25. 25. Crossing over © 2012 Pearson Education, Inc.
  26. 26. Non-disjunction = Nonseparation of chromoso mes resulting in diploid or empty gametes.
  27. 27. Conditions caused by non-disjunction Downs syndrome = Trisomy 21 - 3 copies of chromosomes 21 equalling a total of 47 chromosomes. = 2n + 1(chance of occurring in oogenesis increases with maternal age) Turners syndrome = Monosomy X - has only one X chromosomes totalling only 45 chromosomes in her body cells. (monosomy X) = 2n-1 Klinefelter’s syndrome = XXY - male which has an extra X chromosome = 2n + 1
  28. 28. Down’s syndrome – trisomy 21 A simple check for the presence of a bone in the nose could more accurately test unborn babies for Down's syndrome, scientists say. Researchers say combining the nose test with existing screening methods (amniocentesis, CVS) could lead to a five-fold reduction in the number of miscarriages linked to an invasive procedure used to confirm Down's syndrome.
  29. 29. Klinefelter’s syndrome XXY Normal boy who develops some female secondary sex character-istics at puberty. -slightly lower IQ, infertile, delayed motor, speech, maturation -treated with

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