Lecture Notes: Variation in Biological Populations

Introduction to Variation

• Variation among individuals can be studied at the protein level.
• Phenotypic differences can be observed in organisms like fruit flies and humans.

Techniques to Study Variation

Protein Level Variation

• Starch Gel Electrophoresis
  • A historical molecular technique used to study proteins.
  • Involves running an electric current through a starch gel with tissue samples.
  • Proteins migrate through the gel based on their electric charge.
  • Different forms of proteins, called allozymes, can be distinguished.
  • Underestimates variation as it might not show all protein differences.
  • Variations may exist at the DNA level that don’t affect protein structure.

DNA Level Variation

• Mutations in DNA can lead to variations such as different alleles.
• Single nucleotide differences can affect protein migration in electrophoresis.
• Restriction enzyme analysis used for detecting variable sites in DNA.

Geographic Variation

Examples

• Flicker Population

  • Red-shafted and yellow-shafted flickers show genetic and phenotypic differences.
  • Considered a single species due to allele exchange.

• Potentilla glandulosa (Plant Subspecies)

  • Variation in height observed among subspecies at different elevations.
  • Study shows differences due to genetic and environmental effects.

Clinal Variation

• Definition: Gradual change in phenotype or allele frequencies over geographic areas.
• Examples:
  • Alcohol Dehydrogenase Allele Frequencies
    • Gradual change in allele frequencies in Drosophila populations in Australia and North America.
  • Human Skin Color
    • Gradual clinal variation in skin color with distance from the equator.
    • Change in skin reflectance percentage based on latitude.

Conclusion

• Understanding variation is crucial for studying population genetics.
• Different methods and examples illustrate how genetic and environmental factors contribute to variation.