Heredity and Evolution

• Introduction

  • Heredity: Transmission of characters/traits from parents to offspring.
  • Variation: Differences in traits among individuals of the same species.

• Accumulation of Variation during Reproduction

  • Basis for evolution.
  • Occurs during DNA copying (not 100% accurate).
  • Can be useful or harmful; useful variations help survival.

• Heredity (Genetics)

  • Gregor Johann Mendel: Pioneer of genetics (worked on garden peas).
  • Key Terms
    • Trait: Specific characteristic (e.g., tall/short).
    • Allele: Variant form of a gene.
    • Genotype: Genetic makeup of an organism.
    • Phenotype: Observable physical appearance.
    • Dominant Trait: Expressed trait in $F_1$ generation (e.g., T).
    • Recessive Trait: Masked trait in $F_1$ generation (e.g., t).
  • Mendel’s Experiments
    • Monohybrid Cross: Cross considering a single trait (Height).
      • $F_1$ generation: All tall plants.
      • $F_2$ generation phenotypic ratio: 3:1 (Tall:Dwarf).
      • $F_2$ generation genotypic ratio: 1:2:1 (TT:Tt:tt).
    • Dihybrid Cross: Cross considering two traits (Seed shape & color).
      • $F_2$ generation phenotypic ratio: 9:3:3:1.
      • Law of Independent Assortment derived.
  • Mendel's Laws
    • Law of Segregation: Alleles separate during gamete formation.
    • Law of Independent Assortment: Genes for different traits sort independently.

• Sex Determination

  • Mechanisms vary across species (environmental or genetic).
  • Human Sex Determination
    • Total chromosomes: 23 pairs (44 autosomes + 1 pair sex chromosomes).
    • Females: XX (produces eggs with X).
    • Males: XY (produces sperm with X or Y).
    • Child's sex determined by the father's sperm (X or Y fertilizing the egg).

• Evolution

  • Gradual change in living organisms over generations.
  • Acquired vs Inherited Traits
    • Acquired Traits: Developed during lifetime, not passed to progeny (e.g., muscle mass).
    • Inherited Traits: Caused by changes in DNA, passed to progeny (e.g., eye color).
  • Speciation
    • Formation of new species from existing ones.
    • Driven by genetic drift, natural selection, geographical isolation.
  • Evolution and Classification
    • Classification reflects evolutionary relationships.
    • Tracing common ancestry using homologous organs.

• Evidences of Evolution

  • Homologous Organs
    • Same structure, different functions.
    • Indicates divergent evolution and common ancestry (e.g., forelimbs of humans and birds).
  • Analogous Organs
    • Different structure, same function.
    • Indicates convergent evolution (e.g., wings of birds and bats).
  • Fossils
    • Preserved remains of dead organisms.
    • Carbon dating used to determine fossil age.
    • Show transitional stages (e.g., Archaeopteryx linking birds and reptiles).

• Human Evolution

  • All human populations belong to a single species: Homo sapiens.
  • Originated in Africa.
  • Migrated across the globe, adapting to diverse environments.
  • Studied through excavation, carbon dating, DNA sequence studies.