Asexual Reproduction

• Cell theory:

  • All living things are composed of cells
  • All cells come from pre-existing cells by cell division
  • Cell division is necessary to replace cells that have died or been damaged and permit growth
• Three stages of the cell cycle:

  • Interphase: Growth and reproduction
  • Mitosis: Division of the nucleus (2 daughter nuclei with complete DNA formed)
  • Cytokinesis: Division of the cytoplasm and organelles (completes the division - 2 cells formed)
• Interphase:

  • The longest phase
  • Cells grow and perform their normal function
  • Cell prepares to divide by replicating its DNA and organelles
  • DNA is in long, thin strands called chromosomes
  • Chromosomes copy themselves, so each chromosome is made up of 2 identical strands of DNA
  • G: growth of cell
  • R: repair
  • R: replication of chromosomes
• Mitosis:

  • The stage where the nucleus is divided
  • Two copies of the DNA separate to opposite ends of the cell
  • Each new nucleus has the same number of chromosomes and DNA as the original parent cell
  • Cell division is necessary when cells become too large to function properly
• Mitosis only occurs in somatic cells (all cells of the body except for the reproductive cells)

  • Somatic cells in humans contain 46 chromosomes (reproductive cells contain 23)
  • 46 chromosomes are actually 23 pairs of two
• Mitosis is divided into 4 main stages:

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase:

  • DNA condenses to form chromosomes
  • Spindle fibres begin to form
  • The membrane around the nucleus breaks down
  • A chromatid is one copy of a piece of the entire DNA found in a nucleus
• Metaphase:

  • Chromosomes line up in the middle of the cell
  • Centrioles are on opposite ends of the cell with spindle fibres stretching to the centromeres of the chromosomes
• Anaphase:

  • Chromatids break apart at the centromere
  • Chromatids are pulled to opposite sides of the cell by the spindle fibres
• Telophase:

  • 2 daughter nuclei are formed
  • A nucleolus appears in each nucleus
  • Mitosis is complete: the rest of the cell is ready to divide
• After Mitosis:

  • Each cell has an identical copy of all the chromosomes it started with
  • Differentiation explains why cells with the same DNA can look different
• Cytokinesis:

  • The final stage of cell division
  • 2 separate cells are formed
  • Each new daughter cell has a complete copy of the parent’s DNA and its own organelles
• Asexual Reproduction:

  • One parent alone is capable of producing a new individual
  • Genetic information of the offspring is identical to the parent, unless a mutation occurs
  • Organisms that are identical are called clones and can be produced quickly
  • Asexual reproduction leads to low variation in DNA among offspring