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.