Gift thamsanqa lubisi meiosis

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MEIOSIS

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Gift thamsanqa lubisi meiosis

  1. 1. Meiosis.. Edited By: Gift Thamsanqa Lubisi (201209380)
  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. Meiosis • Sex cells divide to produce gametes (sperm or egg). • Gametes have half the # of chromosomes. • Occurs only in gonads (testes or ovaries). Male: spermatogenesis Female: oogenesis • Meiosis is similar to mitosis with some chromosomal differences.
  4. 4. 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.
  5. 5. Homologous chromosome.
  6. 6. 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
  7. 7. Crossing over..
  8. 8. Crossing over.. • Formation of a tetrad while going through the process of crossing-over • This occurs during prophase I of meiosis.
  9. 9. Introduction.. • Meiosis have mainly two division.. Meiosis-I. Meiosis-II.
  10. 10. Interphase I Phases of Meiosis Copyright Pearson Prentice Hall Cells undergo a round of DNA replication, forming duplicate chromosomes.
  11. 11. Copyright Pearson Prentice Hall MEIOSIS I Phases of Meiosis Prophase I Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad.
  12. 12. Crossing Over - variation nonsister chromatids chiasmata: site of crossing over Tetrad variation
  13. 13. Copyright Pearson Prentice Hall Synapsis and Crossing Over in Action
  14. 14. Phases of Meiosis MEIOSIS I Metaphase I Copyright Pearson Prentice Hall Spindle fibers attach to the chromosomes. Tetrads line up in the middle: metaphase plate.
  15. 15. Spindle fibers pull the homologous chromosomes toward opposite ends of the cell. Tetrads split into single chromosomes. MEIOSIS I Anaphase I Copyright Pearson Prentice Hall Phases of Meiosis
  16. 16. Nuclear membranes form. Cell separates into two cells. The two cells produced have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I. MEIOSIS I Telophase I and Cytokinesis Copyright Pearson Prentice Hall Phases of Meiosis
  17. 17. Phases of Meiosis The two cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, neither cell goes through chromosome replication. Each of the cell’s chromosomes has 2 chromatids. Copyright Pearson Prentice Hall Meiosis II
  18. 18. Telophase-1..
  19. 19. Meiosis-II • No interphase.. • Similar to Mitosis…
  20. 20. 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..
  21. 21. Metaphase-II.. • Sister chromatids line up at the middle of the cell..
  22. 22. Anaphase-II.. • The centromeres of sister chromatids finally separate. • The sister chromatids of each pair move toward opposite poles. Now its individual chromosomes.
  23. 23. 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)..
  24. 24. 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
  25. 25. A Comparison of Mitosis and Meiosis • Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell • Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell • The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
  26. 26. Fig. 13-9 MITOSIS MEIOSIS Parent cell Chromosome replication Prophase Chiasma Chromosome replication Prophase I Homologous chromosome pair 2n = 6 Replicated chromosome MEIOSIS I Metaphase Metaphase I Anaphase Telophase Anaphase I Telophase I Haploid n=3 Daughter cells of meiosis I 2n MEIOSIS II 2n Daughter cells of mitosis n n n n Daughter cells of meiosis II SUMMARY Property Mitosis Meiosis DNA replication Occurs during interphase before mitosis begins Occurs during interphase before meiosis I begins Number of divisions One, including prophase, metaphase, anahase, and telophase Two, each including prophase, metaphase, anaphase, and telophase Synapsis of homologous chromosomes Does not occur Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Number of daughter cells and genetic composition Two, each diploid (2n) and genetically identical to the parent cell Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Role in the animal body Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Produces gametes; reduces number of chromosomes by half and introduces genetic variability amoung the gametes
  27. 27. Fig. 13-9a MITOSIS MEIOSIS Parent cell Chromosome replication Prophase Chiasma Chromosome replication Prophase I Homologous chromosome pair 2n = 6 Replicated chromosome MEIOSIS I Metaphase Metaphase I Anaphase Telophase Anaphase I Telophase I Haploid n=3 Daughter cells of meiosis I 2n Daughter cells of mitosis 2n MEIOSIS II n n n n Daughter cells of meiosis II
  28. 28. Reference list: • Gretchen, G. (2012). Meiosis slideshare. Available from: http://www.slideshare.net/gunthergretchen/biologa-meiosis [Accessed 06 March 2014]. • Guest21d4fb. (2010). Meiosis slideshare. Available from: http://www.slideshare.net/guest21d4fb/meiosis-2 [Accessed 06 March 2014]. • Patel, S. (2013). Meiosis slideshare. Available from: http://www.slideshare.net/GIFTTHAMSANQA1663/savedfiles?s_title=meiosis28422102&user_login=Lionheart009 [Accessed 06 March 2014]. • Swan, J. (2011). Meiosis slideshare. Available from: http://www.slideshare.net/jayswan/chapter-13-presentation-6504581 [Accessed 06 March 2014].
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