4.3: Cell Division

• Cell Division - is the process by which a parent cell divides into two or more daughter cells.
• The two major functions of cell division are:

  1. To create body cells or somatic cells that will maintain, replace, and repair worn out cells
  2. To form gametes (eggs and sperm) for sexual reproduction.
• There are two types of cell division:

  • Mitosis
  • Meiosis
• Mitosis - is a process of nuclear division wherein two genetically identical daughter cells with the same number of chromosomes (diploid cells) as their parent cell are produced.
• Diploid Cell - contains two set of chromosomes (2n)
• Haploid Cell - contain only one set of Chromosome. (n)
• Meiosis - is the reduction division that generates sex cells (gametes).
• Meiosis - The parent cell divides into four daughter cells that each contain half the number of chromosomes (haploid cells).
• Karyotype - shows the number of chromosomes of an organism and the corresponding characteristics, arranged in a particular pattern.
• Chromosomal Sex Determination in Females: XX
• Chromosomal Sex Determination in Male: XY
• Chromosomes - are darkly stained bodies within the nucleus consisting of highly coiled and condensed strands of DNA.
• DNA: Deoxyribonucleic acid
• A replicated chromosome is composed of two sister chromatids, where one is the exact copy of the other.
• Kinetochore - the docking site for spindle fibers.
• Cell Cycle - The sequence of growth, DNA replication, and division of a cell.
• The Cell Cycle consists of:

  • Interphase (G1, S and G2) - non dividing stage
  • Mitosis or Meiosis - dividing stage
  • Cytokinesis - dividing of cytoplasm
• Interphase - is when the cell grows, and the organelles double prior to the actual splitting of the nucleus.
• 93% of cell's life is spent in interphase.
• Three Parts of Interphase:

  • Growth 1
  • Synthesis
  • Growth 2
• G1 - is when organelles double.
• Each new cell needs a complete set of Organelles.
• S - when DNA is replicated.
• Each cell needs a complete and identical set of DNA
• G2 - is where proteins needed for Mitosis are produced.
• Mitosis - The process by which the cell nucleus divides into two identical cell nuclei. (Diploid = 2n)
• Diploid - A cell with two copies of each type of chromosome .
• Mitosis occurs in a series of steps:

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Chromatid - doubled to form short thick rods which pair up and line up in the center of the nucleus.
• Prophase - Chromosomes now called chromatids because they doubled to form short thick rods which pair up and line up in the center of the nucleus.
• Prophase - A centromere connects the two halves of the doubled chromatids.
• Prophase - Spindle fibers begin to form.
• Spindle Fiber - a fibrous structure from the cytoplasm which forms to the centriole.
• Prophase - Centrioles move to opposite sides of the cell.
• Prophase - The nuclear membrane breaks down.
• Metaphase - Centromeres of the chromatid pairs line up in the middle of the cell.
• Metaphase Plate - location where the centromeres line up in the center of the cell.
• Metaphase - by the end of this stage chromatids has attached to spindle fibers.
• Anaphase - the spindle fibers pull the chromatids apart.
• Anaphase - This separates each one from its duplicate. These move to opposite sides of the cell.