Cell Division and the Black Death

Gametes and Fertilization

• Gametes: Egg
• Human Cycle: Meiosis (creation of gametes) → Fertilization → Zygote → Mitosis
  • Meiosis creates the gametes (egg and sperm), each containing half the number of chromosomes.
  • Fertilization is the fusion of egg and sperm, forming a zygote.
  • The zygote then undergoes mitosis (cell division) to develop into an organism.

Chromosomes

• Humans have 46 chromosomes in total, organized as 23 pairs.
• Each gamete (egg or sperm) contributes 23 chromosomes.
• Upon fertilization, the zygote receives 23 chromosomes from each gamete, resulting in a total of 46 chromosomes.

Interphase

• Interphase is the preparatory phase before mitosis, consisting of three sub-phases: G₁, S, and G₂.
• G₁ (Gap 1): Rapid growth of the cell.
• S (Synthesis): Growth continues, and DNA synthesis (replication) occurs.
• G₂ (Gap 2): Further growth and final preparations for cell division.

Mitosis

• Mitosis is the process of cell division, resulting in two identical daughter cells.
  1. Prophase:
     • Chromosomes condense and become visible.
     • The nuclear envelope breaks down.
     • The nucleolus disappears.
  2. Prometaphase:
     • Mitotic spindles appear, extending from the centrosomes.
  3. Metaphase:
     • The mitotic spindle is fully developed.
     • Chromosomes line up along the metaphase plate (the equator of the cell).
  4. Anaphase:
     • Sister chromatids (identical copies of each chromosome) are pulled apart and move to opposite poles of the cell.
  5. Telophase:
     • Chromosomes begin to decondense.
     • The nuclear envelope reforms around each set of chromosomes.
  6. Cytokinesis:
     • Cleavage furrow separates the daughter cells, resulting in two distinct cells.

Black Death

• The Black Death was a devastating pandemic in the 14th century that killed approximately half of Europe's population.