Biology

• 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
• Continuous variation gives smooth bell curves, discontinuous variation gives a step-like shape
• Mutation


  Genetic change, a random change in the base sequence of DNA
• Causes of mutation


  • Ionizing radiation (X-rays, gamma rays)
  • Exposure to certain chemicals (tar in tobacco)
• Adaptive feature


  An inherited feature that helps 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 to 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
• Natural selection example


  • Population of beetles with variation in body coloration
  • Brown beetles have better camouflage on brown tree bark
  • Brown beetles more likely to survive and reproduce
  • Proportion of brown beetles increases over generations
• Adaptation


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


  • Development of antibiotic resistant bacteria
  • Some bacteria have genetic mutation that makes them resistant
  • Resistant bacteria survive and reproduce quickly
  • Antibiotic becomes ineffective due to widespread resistance
• Selective breeding


  A process where humans choose individuals with desirable features, breed them together, and select offspring with desired traits over multiple generations
• Selective breeding process


  1. Selection of individuals with desirable features

  2. Crossing these individuals to produce next generation

  3. Selection of offspring showing desirable features

  4. Repeat process over multiple generations
• Selective breeding examples


  • Enhancing disease resistance in food crops
  • Increasing crop yield
  • Improving taste and flavor of fruits
  • Cultivating plants with large or unique flowers
  • Developing cows, goats, sheep that produce lots of milk or meat
  • Breeding chickens that lay large eggs
  • Developing domestic dogs with gentle nature
  • Breeding sheep for better quality wool
  • Breeding horses with fine features and great speed
• Natural selection


  Occurs naturally without human intervention, results in adaptations that enhance survival and reproduction in a specific environment
• Artificial selection


  Occurs with human intervention and selective breeding, often focuses on traits advantageous or desirable from human perspective, can result in rapid changes in traits