Variation and selection

• Variation is the differences between individuals of the same species
• Types of variation


  • Genetic variation
  • Phenotypic variation
• Genetic variation


  Differences in genetics among individuals within the same species
• Examples of genetic variation

  • Blood group
  • Eye color
  • Gender
  • Ability to roll the tongue
• Phenotypic variation


  Variability of phenotypes within a population
• Causes of phenotypic variation

  • Genetic
  • Environmental
• Example of environmental variation


  • Difference in body type between an active person who exercises regularly and has a fit physique and a person who leads a less active lifestyle and may have a less muscular body type
• Causes of genetic variation in populations

  • Mutation
  • Meiosis
  • Random mating
  • Random fertilization
• Types of variation


  • Continuous variation
  • Discontinuous variation
• Continuous variation


  A range of phenotypes between two extremes, caused by both genes and environment
• Examples of continuous variation

  • Body length
  • Body mass
• Discontinuous variation


  A limited number of phenotypes with no intermediates, usually caused by genes only
• Examples of discontinuous variation

  • ABO blood groups
  • Seed shape in peas
  • Seed color in peas
• Mutation


  1. Gene mutation is a random change in the base sequence of DNA

  2. Caused by factors like ionizing radiation and chemicals

  3. Leads to new alleles being formed
• Adaptive features


  • Inherited features that help an organism to survive and reproduce in its environment
• Adaptive features of hydrophytes

  • Wide and flat leaves to increase surface area and absorb sunlight
  • Small roots as they can absorb water directly through leaves and stems
  • Stomata mostly on upper leaf surface for efficient gas exchange
• Adaptive features of xerophytes

  • Thick cuticle on leaves to prevent water loss
  • Stomata in sunken pits to reduce water loss
  • Small needle-shaped leaves to reduce surface area for evaporation
  • Extensive roots to access deeper soil water
  • Thick stems or leaves to store water
• Natural selection


  The process where certain traits become more common in a population over time because they help organisms survive and reproduce better in their environment
• Natural selection


  1. Genetic variation within a population

  2. Many offspring produced

  3. Offspring face struggle for survival including competition for resources

  4. Individuals better adapted to environment have greater chance of reproducing

  5. Individuals pass on their alleles/genetic traits to next generation

  6. Gradual change in population over time
• Adaptation


  The process resulting from natural selection by which populations become more suited to their environment over many generations
• Selective breeding


  A process where humans choose individuals with desirable features, breed them together to produce the next generation, and select offspring showing the desired features
• Selective breeding


  1. Selection by humans of individuals with desirable features

  2. Crossing these individuals to produce the next generation

  3. Selection of offspring showing the desirable features
• Selective breeding in crops


  • Disease resistance
  • Increased yield
  • Drought tolerance
  • Improved taste and flavor
• Selective breeding in animals


  • Cows, goats, sheep producing lots of milk or meat
  • Chickens laying large eggs
  • Domestic dogs with gentle nature
  • Sheep with good quality wool
  • Horses with fine features and great speed
• Natural selection occurs naturally without human intervention, while artificial selection occurs with human intervention and selective breeding
• Natural selection results in adaptations that enhance survival and reproduction in a specific environment, while artificial selection often focuses on traits advantageous or desirable from a human perspective
• Natural selection can lead to gradual change and diversification of species over time, while artificial selection can result in rapid changes in traits within a population over a relatively short period
• Variations are differences between individuals within a population that can be inherited or acquired during an organism's lifetime.
• Natural selection involves three key components: variation, inheritance, and environmental change.
• The process of natural selection is the mechanism by which evolution occurs.