Variation and Evolution Notes

VARIATION

  • Phenotypic differences within a species, such as fur color, eye color, height, and blood types.

CONTINUOUS VARIATION

  • Variation in species due to both genetic and environmental factors.
  • These factors are measurable.
  • Examples:
    • Height
    • Mass
    • Length

DISCONTINUOUS VARIATION

  • Variation in species due to genetic factors only.
  • These factors are not measurable; they are discrete features that can be grouped.
  • Examples:
    • Blood type
    • Eye color
    • Skin color

GRAPHS

  • Continuous variation is represented using histograms or line graphs.
  • Discontinuous variation is represented using bar charts.

CAUSES OF VARIATION OR NEW ALLELE FORMATION

  • Mutation and sexual reproduction bring changes within DNA or genes, potentially resulting in changes within protein structures.
  • Genetic recombination: During this process, male and female chromosomes exchange alleles, forming unique chromosomes or allele combinations.

MUTATIONS

  • Changes within an organism's DNA/genes that may result in different proteins.
  • Caused by factors called mutagens:
    • Radiation and ionizing rays
    • Chemicals (carcinogens – cancer-causing materials)
    • Viruses and bacteria

NATURAL SELECTION AND EVOLUTION

  • Mutations and sexual reproduction lead to variation.
  • Competition for resources such as shelter, food, water, and mates occurs.
  • The more adapted variety will survive and reproduce, while the less adapted variety either dies out or migrates.
  • The more adapted variety passes on its alleles to offspring that display the same phenotype.
  • This process is called natural selection.
  • When natural selection repeats over multiple generations, evolution takes place.
  • Evolution = new species.

EXAMPLES OF NATURAL SELECTION

Antibiotic Resistance in Bacteria

  • Step 1: In a population of bacteria, one bacterium mutates and becomes antibiotic-resistant.
  • Step 2: Antibiotic kills off all bacteria except for the antibiotic-resistant bacterium.
  • Step 3: The antibiotic-resistant bacterium multiplies, forming a population of antibiotic-resistant bacteria.
  • Step 4: Antibiotic-resistant bacteria can transfer their mutation to other bacteria.

Peppered Moths

  • The peppered moth (Biston betularia) is a classic example of natural selection.
  • Before industrialization, light-colored moths were common because they blended with lichen-covered trees, while dark moths were rare.
  • During the Industrial Revolution, pollution darkened tree trunks, giving dark moths a survival advantage, as they were better camouflaged from predators.
  • Over time, the dark variety became more common.
  • After pollution control restored lichens, light-colored moths became dominant again.
  • This demonstrates how environmental changes drive evolution by natural selection, favoring traits that improve survival and reproduction.

NATURAL SELECTION VS. SELECTIVE BREEDING/ARTIFICIAL SELECTION

  • Selective breeding is when humans select two organisms with desired traits and mate them to produce offspring that possess or inherit both desired traits.
  • Comparison:
    • Selective breeding is faster than natural selection.
    • Selective breeding only benefits humans and not the organism itself.
    • Selective breeding depends on humans as the selective pressure.

HYDROPHYTES AND XEROPHYTES

Hydrophytes

  • Plants adapted to living in water.
  • Adaptations:
    • Large air spaces in the spongy mesophyll to keep plants floating.
    • Flexible stems to reduce damage due to water currents.
    • Highly permeable epidermis to allow water absorption.
    • Large number of stomata on the upper surface to increase transpiration rates.
    • Thin cuticle to allow excess evaporation.

Xerophytes

  • Plants adapted to conserving water in scarce conditions.
  • Adaptations:
    • Thick waxy cuticle to reduce evaporation.
    • Small leaves to reduce surface area for evaporation.
    • Long shallow roots or widespread roots to collect more rain or groundwater.
    • Thick leaves and stems to store water.
    • Rolled leaves or sunken stomata to trap moisture.