Cell Division

Cell Division

1. Meiosis

   • Occurs in the life cycle of sexually reproducing organisms
     • Meiosis I
       • Homologues line up side by side at equator (synapsis)
       • When pairs separate, each daughter cell receives one member of the pair
       • Cells are now haploid and each chromosome is composed of two sister chromatids
       • DNA replication occurs before this division (as in mitosis)
       • Prophase I
         • Metaphase I
           • Anaphase I
             • Telophase I
               • Cytokinesis produces 2 daughter cells which are haploid
             • Homologous chromosomes(each still consisting of 2 chromatids)
           • Homologous pairs line up at metaphase plate such that maternal or paternal member
         • Synapsis occurs, nuclear membrane breaks down
     • Meiosis II
       • Each of the four daughter cells produced has the haploid chromosome number and each chromosome is composed of one chromatid
       • No replication of DNA occurs in this division
       • Centromeres divide and sister chromatids migrate to opposite poles to become individual chromosomes
       • Prophase II
         • Metaphase II
           • Anaphase II
             • Telophase II
               • Nuclei form, cytokinesis
             • Centromeres divide and daughter chromosomes migrate
           • Chromosomes line up at the meta phase plate
         • Cells have one member of each homologous pair
   • Cells are diploid at the beginning of meiosis and haploid at the end
   • Reduces chromosome number so that the daughter nuclei receive only one of each kind of chromosome

2. Mitosis

   • Controlled Mitosis
     • Nuclear division in which chromosome number stays constant
     • DNA replication produces duplicated chromosomes
     • sister chromatids are genetically identical
   • Uncontrolled Mitosis
     • CANCER
     • APOTOSIS
       • Is a naturally occurring programmed cell death, that occurs when a cell cannot complete mitosis
       • It plays a role in preventing cancer
   • 4 PHASES
     • Prophase
       • nuclear membrane disappears, centrosomes migrate, spindle fibers appear
     • Metaphase
       • Chromosomes line up at metaphase plate, associated with spindle fibers
     • Anaphase
       • Centromeres divide, sister chromatids migrate to opposite poles
     • Telophase
       • Nuclear membranes form, spindle disappears, cytokinesis occurs

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