Miss Angus Biology Class: Lamarckism

Introduction

• Host: Miss Angus
• Topic: Lamarckism
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Contextual Background on Lamarck

• Pre-genetics (before Mendel)
• Unclear understanding of DNA
• Knew offspring resembled parents, but mechanism unknown

Lamarck's Hypothesis: Inheritance of Acquired Characteristics

• Definition of Inheritance: Passing traits from parents to offspring
• Definition of Acquired: Traits gained during an organism's lifetime

Fundamental Principles

1. Use and Disuse
   • Organisms respond to environmental changes actively
   • Use it: becomes bigger/stronger
   • Disuse: becomes smaller/weaker, may disappear
   • Misconception: Just using a part more doesn’t mean evolutionary change (e.g., can’t grow wings by wanting to fly)
2. Inheritance of Acquired Characteristics
   • Physical, phenotypic changes
   • Phenotypic changes do not alter genotype (e.g., dyeing hair doesn’t change DNA)
   • Lamarck’s belief: physical changes are passed to offspring (e.g., giraffes' neck length)

Example: Giraffes

• Initial short-necked giraffes
• Environment changes (e.g., food out of reach)
• Giraffes stretch necks -> longer necks
• Phenotypic change passed on
• Cycle repeats, next generation has longer necks

Applying in Exams

• Mention both principles in explanations:
  • Use and Disuse: Active physical changes responding to the environment
  • Inheritance of Acquired Characteristics: Changes passed to offspring
• Example: Lizards to snakes:
  • Legs used less -> disappear/smaller (disuse)
  • Trait passed to offspring (inheritance)
  • Response to environment, active change

Terminology Recap

• Lamarckism: Theory of active trait change and inheritance
• Phenotype: Observable traits
• Genotype: Genetic makeup
• Use/Disuse Principle: Structure becomes stronger with use, weaker with disuse
• Acquired Characteristics: Traits gained during lifetime, thought by Lamarck to be inheritable

Conclusion

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