Lecture on Meiosis and Mitosis

Overview

• Context: Part of a biology MCAT playlist
• Focus: Understanding meiosis, its importance in making gametes for ovaries and testicles
• Connection: Builds on previous discussion on mitosis

Cell Cycle

• Interphase:
  • G1: Growth
  • S: DNA synthesis (replication)
  • G2: Another growth phase
• M Phase:
  • Mitosis or Meiosis occur

Mitosis vs. Meiosis

• Mitosis:
  • Occurs in somatic cells
  • Not involved in sexual reproduction
  • Produces two diploid (2n) identical daughter cells
  • One round of division: prophase, metaphase, anaphase, telophase
• Meiosis:
  • Occurs in sex cells (gametes)
  • Involved in sexual reproduction
  • Produces four haploid (n) non-identical daughter cells
  • Two rounds of division:
    • Round 1 (Reduction Division): Prophase I, Metaphase I, Anaphase I, Telophase I
    • Round 2 (Equatorial Division): Prophase II, Metaphase II, Anaphase II, Telophase II

Phases of Meiosis

Meiosis I

• Prophase I:
  • Crossing over between homologous chromosomes (not sister chromatids)
  • Formation of recombinant chromosomes
  • Responsible for genetic diversity
• Metaphase I:
  • Tetrad alignment at the equatorial plate
  • Chromosomes attached to spindle fibers from only one side
• Anaphase I:
  • Disjunction (separation) of homologous pairs
• Telophase I:
  • Formation of nuclear membrane
  • Two haploid cells produced

Meiosis II

• Similar to mitosis but starts with haploid cells

Genetic Variation

• Crossing Over:
  • Occurs at prophase I
  • Leads to genetic variety among offspring
• Disjunction:
  • Occurs in anaphase
  • Mendel’s first law of segregation is based on this

Non-disjunction and Syndromes

• Non-disjunction: Failure of chromosomes to separate properly
  • Can lead to conditions like Turner Syndrome (45 chromosomes) and Down Syndrome (47 chromosomes, trisomy 21)
  • Also affects sex chromosomes (e.g., Klinefelter Syndrome)

Mendelian Laws

• Mendel’s First Law: Law of Segregation
  • Based on disjunction (separation) during anaphase
• Mendel’s Second Law: Independent Assortment
  • Based on crossing over during prophase

Additional Concepts

• Gene Unlinking and Centimorgans:
  • Measures genetic distance using centimorgan units
• Kinetoplast and Kinetoscope:
  • Kinetoplast: network of circular DNA in certain parasites
  • Kinetoscope: Early motion picture device

Conclusion

• Summary of key differences between mitosis and meiosis
• Importance of genetic diversity through meiosis

Additional Resources

• Anti-cancer pharmacology course and other biology notes available online
• Encouragement to review courses and support further learning

Note: Always refer to additional study materials for comprehensive understanding.