Lecture 6 Cell Division [Meiosis]


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Lecture 6 Cell Division [Meiosis]

  1. 1. BASIC BIOLOGY BIO 101/4 Cell division Meiosis 23 Jan 2007
  2. 2. What is meiosis? <ul><li>Meiosis is a type of cell division. </li></ul><ul><li>Occurs in gamete cell. </li></ul><ul><li>There is a single DNA replication, followed by 2 nuclear divisions. </li></ul><ul><li>Each of the resulting daughter cells has one half of the number of chromosomes as the parent cell. </li></ul><ul><li>From Diploid (2n)  Haploid (n) </li></ul>
  3. 3. <ul><li>Occur at sexual reproduction (gamete cells) </li></ul><ul><li>Will produce haploid (n) gamete cells </li></ul>Ovary Anther Plant Ovary Testis Animal Female Male Organ Eggs cell Pollen Plant Ovum Sperm Animal
  4. 4. <ul><li>Meiosis is divided into two part </li></ul><ul><ul><li>Meiosis I </li></ul></ul><ul><ul><li>Meiosis II </li></ul></ul>
  5. 5. <ul><li>How it become haploid (n)? </li></ul><ul><li>Parent cell with diploid (2n) requires two cell division, result in 4 daughter cells (n). </li></ul><ul><li>Continuous processes </li></ul><ul><ul><li>Meiosis I </li></ul></ul><ul><ul><ul><ul><ul><li>Prophase I </li></ul></ul></ul></ul></ul><ul><li>Metaphase I </li></ul><ul><li>Anaphase I </li></ul><ul><li>Telophase I </li></ul><ul><ul><li>Meiosis II </li></ul></ul><ul><ul><ul><li>Prophase II </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Metaphase II </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Anaphase II </li></ul></ul></ul></ul></ul><ul><ul><ul><li> Telophase II </li></ul></ul></ul>
  6. 6. Term <ul><li>Homologous chromosome </li></ul><ul><li>Chromosome with the similar size, shape and the position of their centromeres. </li></ul><ul><li>Synapsis </li></ul><ul><li>Condition of chromosome pairing </li></ul><ul><li>Bivalent </li></ul><ul><li>Structure of homologous pair </li></ul><ul><li>Tetrad </li></ul><ul><li>Homologous chromosome that have 4 chromatids </li></ul><ul><li>Sister chromatid </li></ul><ul><li>Chromatid from same homologous chromosome </li></ul><ul><li>Chiasma </li></ul><ul><li>Point at which crossing over occur </li></ul>
  7. 7. Bivalent
  8. 10. Stages of meiosis I <ul><li>Reduction division </li></ul><ul><li>It reduces the number of chromosome from 46 (2n) to 23 (n). </li></ul><ul><li>The cell divide has homologous pair of chromosome. </li></ul><ul><li>One homolog comes from mother (maternal) and one from father (paternal). </li></ul><ul><li>When meiosis begins, DNA of each homologous replicates, forming two chromatids joined at two centromeres. </li></ul>
  9. 11. <ul><li>Prophase I </li></ul><ul><li>Duplicated chromosomes condense and become visible. </li></ul><ul><li>Pairing up of homologous chromosomes forming bivalent. This process is called synapsis. </li></ul><ul><li>Synapsis cause the homologous chromosomes closely associated. </li></ul><ul><li>Both homologous chromosomes interwine at chiasma and this process is known as crossing over. </li></ul><ul><li>Crossing over causes exchange the genetic material (DNA) between paternal and maternal chromosomes. </li></ul>
  10. 12. <ul><li>6. Crossing over produces new combination of genes. </li></ul><ul><li>7. The genetic recombination from this process greatly </li></ul><ul><li>enhance the genetic variation. </li></ul><ul><li>8. Spindle fibers are form. </li></ul><ul><li>9. Nuclear envelope breaks down. </li></ul>
  11. 14. <ul><li>Metaphase I </li></ul><ul><li>Homologous chromosomes line up at the equator of the cell. </li></ul><ul><li>Form double rows of homologous chromosomes. </li></ul><ul><li>Unipolar spindle attachment to single kinetochore at each homologue. </li></ul>
  12. 15. <ul><li>Anaphase I </li></ul><ul><li>Homologous chromosomes separate and move to opposite poles of the cell. </li></ul><ul><li>Sister chromatids remain attached at their centromeres. </li></ul>
  13. 16. <ul><li>Telophase I </li></ul><ul><li>One of each pair of homologous chromosomes is at each pole. </li></ul><ul><li>Cytokinesis occur. </li></ul><ul><li>The nuclear envelope reforms and the nucleoli reappear. </li></ul>
  14. 18. Stages in meiosis II <ul><li>Equational division </li></ul><ul><li>Same like mitosis. </li></ul><ul><li>Produce 4 daughter cells with haploid (n) number of chromosomes. </li></ul>
  15. 19. <ul><li>Prophase II </li></ul><ul><li>The chromosomes are again condensed and visible, become short and thick. </li></ul><ul><li>Nucleolus and membrane nucleus dissapear. </li></ul><ul><li>Centriole move to opposite poles. </li></ul><ul><li>DNA does not replicate again. </li></ul>
  16. 21. <ul><li>Metaphase II </li></ul><ul><li>Chromosomes line up at the equator of the cell. </li></ul><ul><li>Anaphase II </li></ul><ul><li>Centomere separation occurs. </li></ul><ul><li>Chromatids moves to opposite poles. </li></ul><ul><li>Telophase II </li></ul><ul><li>Nuclei formed at opposite poles of each cell. </li></ul><ul><li>Chromosomes gradually elongate to form chromatin fibers. </li></ul><ul><li>Cytokinesis occurs. </li></ul><ul><li>Four haploid cells are produced. </li></ul>
  17. 23. Importance of meiosis <ul><li>For sexual reproduction. </li></ul><ul><li>Maintains the chromosome numbers constant from generation to generation. </li></ul><ul><li>Assures a different genetic make up for the next generation as a result of crossing over and new combination of genes. </li></ul>
  18. 24. Comparison between mitosis and meiosis Meiosis Mitosis Chiasma form and crossing over occurs during prophase I. Chiasma are never formed and crossing over never occurs. Homologous chromosomes associated to form bivalen during prophase I. Chromosomes do not associate during prophase. DNA replicates once during S phase of interphase but there are two successive nuclear division. DNA replicates once during the S phase of interphase, and nucleus divides once. Only in sexual reproduction cell, gamete cell Occurs in somatic cell in all parts of the body Dividing cells are diploid Dividing cells can be diploid or haploid
  19. 25. 4 daughter cells are formed. In male human, 4 sperm cells are formed. In female human, one ovum and 3 polar bodies are formed. 2 daughter cells are formed. Daughter cells are genetically different from parental cell. In the absence of mutation, daughter cells are genetically identical to parental cell. Daughter cells have only half the number of chromosomes found in the parent cell. Daughter cells have the same number of chromosomes as the parent cell. Chromosomes move to opposite poles during anaphase I. Chromatids move to opposite poles during anaphase. Chromosomes form two rows at the equator of the cell during metaphase I. Chromosomes form a single row at the equator of the cell during metaphase. Meiosis Mitosis
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