Unit 2: Genetics and Evolution

Chapter 3: Evolution

Origin of Life

• Oparin-Haldane Theory: Life originated from non-living organic molecules in a reducing atmosphere.
• Miller-Urey Experiment (1953):
  • Experimentally supported the Oparin-Haldane theory.
  • Produced amino acids and other organic molecules from inorganic precursors.

Evidences of Evolution

• Homologous Organs: Same origin, different function (Divergent evolution).
• Analogous Organs: Different origin, same function (Convergent evolution).
• Embryology: Similarities in embryos (e.g., gill slits).
• Fossils: Direct evidence of past life.
• Biogeography: Distribution of species (e.g., Darwin's Finches).
• Molecular Evidence: Similarities in DNA and proteins.

Darwin’s Theory of Natural Selection

1. Overproduction: More offspring are produced than can survive.
2. Struggle for Existence: Competition for resources.
3. Variation: Individuals in a population vary.
4. Survival of the Fittest: Individuals with advantageous traits survive and reproduce.
5. Speciation: Accumulation of variations leads to new species.

Neo-Darwinism (Modern Synthesis)

• Combines Darwinian selection with Mendelian genetics.
• Sources of Variation:
  • Mutation: The ultimate source of new alleles.
  • Recombination: Shuffles existing alleles.
• Mechanisms of Evolution:
  • Natural Selection
  • Gene Flow
  • Genetic Drift (Founder & Bottleneck effects)

Hardy-Weinberg Principle

• Allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
• Equation: p² + 2pq + q² = 1
• Evolution occurs when equilibrium is disturbed by:
  • Natural Selection, Gene Flow, Genetic Drift, Mutation, Non-random mating.

Types of Natural Selection

• Directional Selection: Favors one extreme phenotype.
• Disruptive Selection: Favors both extreme phenotypes.
• Stabilizing Selection: Favors the intermediate phenotype.

Adaptive Radiation

• Evolution of different species from a common ancestor in a given geographical area.
• Examples:
  • Darwin's Finches: Diversified beak shapes on the Galapagos Islands.
  • Australian Marsupials: Evolved into diverse forms from a common ancestor.

Human Evolution

• Dryopithecus (ape-like)
• Australopithecus (walked upright)
• Homo habilis (first human-like, tool user)
• Homo erectus (used fire)
• Neanderthal Man (buried their dead)
• Homo sapiens (modern humans)