Cell Division, Cell Diversity and Cellular Organization

• What is the Cell Cycle?

  G1 - Cell grows in size, Orgnelles replicate

  G1 Checkpoint - Checks for adequate growth

  S Phase - All DNA is replicated

  G2 Checkpoint - DNA is checked for errors

  G2 - Cell continues to grow

  Mitosis - Cell divides

  G0 - New cells checked for errors, Checked for differentiation

  
• What are the functions of Mitosis?

  • Produces 2 diploid cells
  • Aasexual reproduction
  • Tissue repairs
  • Produces 2 genetically identical daughter cells
• The Stages of Mitosis:

  Prophase - Nuclear envelope breaks down, chromosomes condense and become visible, and centrioles move to poles

  Metaphase - Chromosomes line up on the equator, and spindle fibers attach to centromeres of chromosomes

  Anaphase - Chromosomes break at centromeres, sister chromatids move to opposite poles, and spindle fibers shorten

  Telophase - Separated chromatids reach opposite poles, the nuclear envelope begins to reform around each new set of chromosomes, and cells now contain 2 diploid nuclei, each genetically identical to one another. Than cytokinesis occurs
• Cytokinesis: The division of cytoplasm into two separate cells.
• What are the functions of Meiosis?

  • Produces 4 haploid cells
  • 2 Divisions (1 Reduction division)
  • Making sex cells
  • Four genetically unique daughter cells
  • Produces variation (P1, M1, M2)
• In Meiosis Prophase I, DNA condenses and becomes visible as chromosomes.
• The chromosomes are arranged side by side in homologous pairs.
• A pair of homologous chromosomes is called a bivalent.
• As the homologous chromosomes are very close together the crossing over of non-sister chromatids may occur.
• The point at which the crossing over occurs is called the chiasma.
• In this stage centrioles migrate to opposite poles and the spindle is formed.
• The nuclear envelope breaks down in Meiosis Metaphase I.
• The bivalents line up along the equator of the spindle, with the spindle fibres attached to the centromeres.
• The maternal and paternal chromosomes in each pair position themselves independently of the others; this is independent assortment.
• This means that the proportion of paternal or maternal chromosomes that end up on each side of the equator is due to chance.
• In Meiosis Anaphase I, the homologous pairs of chromosomes are separated as spindle fibers pull whole chromosomes to opposite ends of the spindle.
• The centromeres do not divide in Meiosis Telophase I.
• The chromosomes arrive at opposite poles in Meiosis Telophase I.
• Spindle fibres start to break down in Meiosis Telophase I.
• During Prophase II, the nuclear envelope breaks down and chromosomes condense.
• Metaphase II in meiosis involves chromosomes lining up in a single file along the equator of the spindle.
• Anaphase II in meiosis involves centromeres dividing and individual chromatids being pulled to opposite poles.
• The process of Anaphase II in meiosis creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell.
• Telophase II in meiosis involves nuclear membranes forming around each group of chromosomes.