Lecture Notes: Asexual and Sexual Reproduction

Introduction to Reproduction

• Two types of reproduction: Asexual and Sexual
• Common misconception: Humans don't do asexual reproduction - they do, but not for producing new individuals.
• Prokaryotes (bacteria, archaeans): Single chromosome doubles and splits into two cells (binary fission)
  • Organelles with own DNA: Mitochondria and chloroplasts undergo binary fission

Asexual Reproduction

Binary Fission

• Prokaryotes: Chromosome doubles and splits into two
• Organelles: Mitochondria and chloroplasts
• Protists: Similar process due to different chromosomes

Parthenogenesis

• Definition: Development from an unfertilized egg
• Examples:
  • Aphids
  • Carpenter bees, crayfish
  • Sharks, Komodo dragons

Mitosis

• Functions: Growth, replacement, repair of cells
• Examples:
  • Animal cells like hydra and sea stars
  • Sea stars can regenerate from a broken arm
  • Human examples: Skin, red blood cells (bone marrow)

Plant Examples

• Spider plants: Send out runners forming new plants
• Maternity plant: Produces plantlets on leaf edges
• Bulbs/Corms: Garlic cloves, tulip separation
• Crabgrass: Rhizomes connect plants across yards
• Strawberry plants:
  • Asexual reproduction: Through runners
  • Sexual reproduction: Seeds in strawberries from flowers

Sexual Reproduction

Animal Life Cycle

• Process: Involves both mitosis and meiosis
• Diploid (2n) and Haploid (n):
  • Adults: 2n (46 chromosomes)
  • Gametes: n (23 chromosomes)
• Fertilization: Combines haploid gametes to form diploid zygote (fertilized egg)

Plant Life Cycle (Mosses)

• Sporophyte: 2n, produces spores via meiosis
• Spores: 1n, undergo mitosis to become gametophytes
• Gametophyte: Produces gametes (sperm and egg)
• Fertilization: Forms diploid zygote within 1n haploid plant

Key Concepts

• Mitosis: Produces identical cells (used for growth and repair)
• Meiosis: Reduces chromosome number by half (essential for sexual reproduction)
• Fight: Terminology in plant division names
• Sporophyte and Gametophyte: Different functions in plant reproduction

Summary

• Asexual reproduction involves creating identical cells or individuals without genetic exchange
• Sexual reproduction involves the combination of genetic material from two parents to produce genetically unique offspring
• Different organisms and even parts of organisms can reproduce asexually or sexually depending on conditions and necessities.