Cell Division - Meiosis


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It is the presentation on the MEIOSIS phase of the Cell division.

It includes all the details and definitions that are related to the topic of meiosis with the labelled diagrams.

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Cell Division - Meiosis

  1. 1. Meiosis.. Prepared By: Shivang Patel..
  2. 2. Introduction.. • A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. • Diploid – 2 sets of chromosomes. It is the term used to refer to a cell that contains both sets of homologous chromosomes. • Haploid – 1 set of chromosomes. it is the term used to refer to a cell that contains only a single set of chromosomes.
  3. 3. Homologous chromosome…. Homologous - term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent. Homologous chromosomes are similar in shape, position and information, but not identical to each other.
  4. 4. Homologous chromosome.
  5. 5. Important definitions.. • Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. • Tetrad - structure containing 4 chromatids that forms during meiosis. • crossing-over - process in which homologous chromosomes exchange portions of their chromatids during meiosis
  6. 6. Crossing over..
  7. 7. Crossing over.. • Formation of a tetrad while going through the process of crossing-over • This occurs during prophase I of meiosis.
  8. 8. Introduction.. • Meiosis have mainly two division.. Meiosis-I. Meiosis-II.
  9. 9. Prophase I 1.Occupies 90% of meiosis 2.Chromosomes begin to condense 3.Homologous chromosomes loosely pair along their length precisely aligned gene by gene • In crossing over, DNA molecules rejoin each other
  10. 10. Prophase-1.
  11. 11. Prophase-1 • Each chromosome pair is visible (microscope) as a tetrad: 4 chromatids • Each tetrad has one or more chiasmata (regions where crossing over occurred), hold the homologues together until anaphase I • Centrosomes movement, spindle microtubules formation, nuclear envelope breakdown & nucleoli dispersal occur as in mitosis. • In late prophase I, kinetochores of each homologue attach to microtubules from one pole or the other • Then, homologous pairs move toward the metaphase plate.
  12. 12. Metaphase-1. • Pair of homologous chromosomes (form of tetrads) are arranged on metaphase plate, with one chromosome of each pair facing each pole • Both chromatids of a homologue are attached to kinetochore microtubules from one pole; those of the other homologue are attached to microtubules from the opposite pole..
  13. 13. Metaphase-1..
  14. 14. Anaphase-1. 1. Chromosomes move toward poles.. 2. Sister chromatids remain attached at centromere & move as a single unit toward same pole.. 3. Homologous chromosomes, each composed of 2 sister chromatids, move toward opposite poles..
  15. 15. Anaphase-1..
  16. 16. Telophase-1 1. At beginning of telophase I, each half of the cell has a complete haploid set of chromosomes 2. But each chromosome is still composed of 2 sister chromatids
  17. 17. Telophase-1..
  18. 18. Meiosis-II • No interphase.. • Similar to Mitosis…
  19. 19. Prophase-II.. • Cells have one set of sister chromatids • Nuclear membrane breaks down • Centrioles separate. • Each of the daughter cells forms a spindle, and the double stranded chromosomes moves towards the equator..
  20. 20. Metaphase-II.. • Sister chromatids line up at the middle of the cell..
  21. 21. Anaphase-II.. • The centromeres of sister chromatids finally separate. • The sister chromatids of each pair move toward opposite poles. Now its individual chromosomes.
  22. 22. Telophase-II.. • Cells start to split in two • Each cell has one set of chromosomes—it is a haploid • Nuclei form at opposite poles of the cell and cytokinesis occurs. • After completion of cytokinesis there are four daughter cells. • All are haploid (n)..
  23. 23. Overview of Meiosis-I..
  24. 24. Overview of Meiosis-II…
  25. 25. Non-Disjunction.. • Non-disjunction is the failure of homologous chromosomes, or sister chromatids, to separate during meiosis. • Non-disjunction results with the production of zygotes with abnormal chromosome numbers…… remember…. An abnormal chromosome number (abnormal amount of DNA) is damaging to the offspring.
  26. 26. Impacts of Non-Disjunction.. • The first is called Monosomy, the second is called Trisomy. If an organism has Trisomy 18 it has three chromosomes in the 18th set, Trisomy 21…. Three chromosomes in the 21st set. If an organism has Monosomy 23 it has only one chromosome in the 23rd set.
  27. 27. Common non disjunction disorder.. • • • • Down’s Syndrome – Trisomy 21 Turner’s Syndrome – Monosomy 23 (X) Kleinfelter’s Syndrome – Trisomy 23 (XXY) Edward’s Syndrome – Trisomy 18