Cellular Reproduction

Cloning, anyone?

What is the purpose of reproduction?

A. Modes of reproduction

  1. Asexual reproduction
  2. Sexual reproduction
    1. Syngamy: identical gametes
      • Many protozoa, algae, fungi
    2. Fertilization: egg & sperm
      • Plants, animals

B. Reproduction of a cell

What are genes? Where are they found?


  1. DNA wrapped around histone proteins (eukaryotes): chromatin
  2. Chromosomes condense only during cell division

The cell cycle

  1. G0: non-dividing cells
  2. Interphase: Preparation for division
  3. M phase: Mitosis (nucleus divides)
  4. Cytokinesis: cell divides
  5. Cell cycle checkpoints & signals
  6. Cancer: loss of cell cycle control

C. Sexual reproduction: Meiosis

How many chromosomes do our cells have?

Life cycle of sexual organisms

  1. Fertilization: zygote (2N)
  2. Gametogenesis: sperm & egg (N)
  3. Alternation of generations


  1. Meiosis consists of 2 cell divisions
  2. Meiosis I reduces the number of chromosomes to 1/2
  3. Interkinesis
  4. Meiosis II separates sister chromatids
  5. Meiosis produces 4 distinct gametes

Origins of genetic diversity

  1. Random assortment of chromosomes
  2. Crossing over
  3. Random fertilization
  1. In-vitro fertilization
  2. Cloning - human or otherwise
  3. Genetic testing - heritable traits
  4. Chromosomal abnormalities: nondisjunction
  5. Cancer