Lecture Notes: Mitosis vs. Meiosis

Overview

• Mitosis and Meiosis are processes by which cells divide, but they have different functions and outcomes.
• Mitosis is a cycle that results in the creation of two identical cells, while Meiosis creates gametes (sex cells) with half the number of chromosomes.

Mitosis

• Starting Cell: Diploid number of chromosomes (2n). For humans, this means 46 chromosomes.
  • 23 chromosomes from the mother and 23 from the father, forming 23 homologous pairs.
• Process:
  • The cell undergoes the cell cycle, growing and replicating its DNA and centrosomes.
  • After mitosis and cytokinesis, two identical cells are produced, each with 2n chromosomes (46 for humans).
  • These cells can enter the cell cycle again, repeating the process.
• Purpose:
  • Allows growth and repair by producing identical somatic (body) cells.
  • Contributes to the development of a single-cell organism into a multicellular organism like humans.

Meiosis

• Starting Cell: Also begins with a diploid number of chromosomes (2n).
• Process: Occurs in two phases - Meiosis I and Meiosis II.
  • Meiosis I:
    • The cell replicates its DNA.
    • Results in two cells with a haploid number of chromosomes (n). Homologous pairs are split; each cell gets a random mix of maternal and paternal chromosomes.
  • Meiosis II:
    • Similar to mitosis, but cells start with a haploid number.
    • Results in four cells, each with a haploid chromosome number, and potentially different genetic information.
• Outcome:
  • Produces gametes (sex cells): sperm in males, eggs in females.
  • These cells are used for fertilization in sexual reproduction, combining to form a new organism.
• Characteristics:
  • Not a cycle like mitosis; results in sex cells that don't divide further but fuse with other gametes during fertilization.

Biological Context

• Mitosis occurs in somatic cells, which make up the bulk of the body.
• Meiosis occurs in germ cells, located in the testes of males and ovaries of females.
  • Germ cells can undergo mitosis to produce more germ cells or meiosis to produce gametes.

Key Differences

• Mitosis: Produces identical cells for growth and repair.
• Meiosis: Produces genetically diverse gametes for reproduction.

Applications

• Mitosis: Critical for tissue growth and healing.
• Meiosis: Essential for producing diversity in sexual reproduction.

Understanding these processes is crucial for grasping the fundamental mechanisms of human development and reproduction.