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Meiosis

Meiosis. https:// www.khanacademy.org/science/biology/cellular-molecular-biology/meiosis/v/chromosomal-crossover-in-meiosis-i. What is Meiosis Exactly?. Meiosis is a form of cell division that halves the number of chromosomes when forming specialized reproductive cells such as gametes or spores

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Meiosis

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  1. Meiosis https://www.khanacademy.org/science/biology/cellular-molecular-biology/meiosis/v/chromosomal-crossover-in-meiosis-i

  2. What is Meiosis Exactly? • Meiosis is a form of cell division that halves the number of chromosomes when forming specialized reproductive cells such as gametes or spores • There are 2 stages of meiosis, Meiosis 1 and meiosis 2 • Meiosis 1 and 2 create 4 haploid cells all together

  3. IV. Meiosis – Reduction Division

  4. Stages of Meiosis 1

  5. Stages of Meiosis 2

  6. Interphase before replication

  7. Interphase after replication

  8. I. Meiosis (Reduction Division) A. Meiosis I 1. Prophase I a. chromosomes become distinct b. nucleolus and nuclear membrane disappear and spindle fibers appear

  9. Prophase I c. spindle fibers appear d.synapsis–homologous chromosomes Line up together

  10. Prophase I e. crossing over may occur 1) portions of chromatid from one parent break off and attach to a homologous chromatid from the other parent 2) results in genetic recombination

  11. 2. Metaphase I a. chromosomes line up along the midline b. sister chromatids do not separate

  12. 3. Anaphase I a. at random, one member of each homologous pair moves to the opposite poles (independent assortment

  13. 4. Telophase I and Cytokinesis I a. chromosomes reach opposite poles b. cytokinesis begins

  14. Telophase I c. resulting cells have the n or haploidnumber of chromosomes 1) one member of each homologous pair with two attached chromatids d. each new cell contains ½ the the number of chromosomes as the original cell

  15. B. Meiosis II 1. Prophase II a. spindle form and chromosomes begin to move toward the mid-line of the cell

  16. . Metaphase II a. chromosomes move to the mid-line of the dividing cell

  17. 3.Anaphase II a. chromatids separate and move to the opposite poles of the cell

  18. 4. Telophase II a. nuclear membrane forms around the nucleus in each cell b. each resulting cell contains the n number of chromosomes

  19. Meiosis 1 and Meiosis 2

  20. Animation of meiosis

  21. Mitosis 2 cells result One division 2n number of chromosomes in resulting cells Meiosis 4 cells result Two divisions n number of chromosomes in resulting cells C. Chart Comparing Mitosis and Meiosis

  22. D. Genetic Recombination and Variation 1. independent assortment 2. crossing over 3. random fusionof sperm and egg

  23. E. Formation of Gametes 1. spermatogenesis – results in 4 viable sperm 2. oogenesis – results in 1 egg and 3 polar bodies

  24. Spermatogenesis

  25. Oogenesis

  26. Fertilization [sperm (n) + egg (n)  zytote (2n) ]

  27. Asexual One parent Identical genetic material Mitosis, budding, binary fission Sexual Two parents Different genetic material Meiosis + fertilization F. Sexual vs Asexual Reproduction

  28. Meiosis creates genetic variation • During normal cell growth, mitosis produces daughter cells identical to parent cell (2n to 2n) • Meiosis results in genetic variation by shuffling of maternal and paternal chromosomes and crossing over. No daughter cells formed during meiosis are genetically identical to either mother or father During sexual reproduction, fusion of the unique haploid gametes produces truly unique offspring.

  29. Karyotype 1. picture of homologous chromo- somes and sex chromosomes 2. used to detect chromosome abnormalities

  30. Homologues • Chromosomes exist in homologous pairs in diploid cells. Exception: Sex chromosomes (X, Y). Other chromosomes are known as autosomes, they have homologues.

  31. Human Chromosomes

  32. In humans … • 23 chromosomes donated by each parent (total = 46 or 23 pairs). • Gametes (sperm/ova): • Contain 22 autosomes and 1 sex chromosome. • Are haploid (haploid number “n” = 23 in humans). • Fertilization/syngamy results in zygote with 2 haploid sets of chromosomes - now diploid. • Diploid cell; 2n = 46. (n=23 in humans) • Most cells in the body produced by mitosis. • Only gametes are produced by meiosis.

  33. In humans e.g. 23 chromosomes in haploid 2n = 46; n = 23 2n = 223 = ~ 8 million possible combinations!

  34. Random fertilization At least 8 million combinations from Mom, and another 8 million from Dad … >64 trillion combinations for a diploid zygote!!!

  35. Karyotyping- normal

  36. Down's Syndrome

  37. some of the previous slides came from the following website • http://cchs.churchill.k12.nv.us/marshk/Notes/meiosis.ppt#352,39,Slide 39

  38. www.biology.Arizona.edu/

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