Lecture on Cell Division: Mitosis and Meiosis

Introduction

• Every human starts as a single cell, a zygote, formed from the fertilization of sperm and egg.
• This single cell divides into billions of cells through a process known as mitosis.

Mitosis

• Definition: A type of cell division that results in two genetically identical diploid daughter cells.
• Process:
  • Begins with a single cell containing 46 chromosomes (diploid).
  • DNA replicates, doubling chromosomes from 46 to 92.
  • Cell splits into two, each with 46 chromosomes.
• Significance:
  • Essential for growth and repair of tissues.
  • Continues throughout life as cells are continuously replaced (e.g., skin cells, stomach lining).
  • Used in asexual reproduction (e.g., bacteria) and cloning.
• Examples:
  • Lose and replace 40,000 skin cells per minute.
  • Entire stomach lining replaced every month.

Meiosis

• Definition: A type of cell division that results in four genetically different haploid cells.
• Process:
  • Involves two division cycles.
  • Starts with a diploid cell, DNA replicates, then divides twice.
  • Ends with four haploid cells, each with 23 chromosomes.
• Significance:
  • Creates genetic variation among offspring.
  • Necessary for sexual reproduction.
  • Random fertilization increases variation.
• Examples:
  • Haploid cells are gametes (sperm and egg), each with 23 chromosomes.
  • Fertilization restores diploid number (46 chromosomes) in a zygote.

Comparison of Mitosis and Meiosis

• Mitosis:
  • Produces two diploid daughter cells from one diploid cell.
  • Used for growth, repair, and asexual reproduction.
• Meiosis:
  • Produces four haploid cells from one diploid cell.
  • Used for sexual reproduction to create genetic diversity.

Conclusion

• Mitosis and meiosis are crucial processes for life.
• Mitosis is for cellular replication and maintenance, while meiosis is for reproductive diversity.

Review

• Consider ten true or false questions to ensure understanding of the topic.