17.1.1

Phenotypic Variation

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Variations in Populations

Genetic diversity is important as it allows species to respond to change. Species with limited genetic diversity are at greater risk of extinction.

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Genetic variation

  • Individuals of a population often display different phenotypes, or express different alleles of a particular gene.
    • E.g. A golden retriever looks completely different from a pug but they are both part of the species Canis familiaris.
  • These differences are called polymorphisms.
  • The distribution of phenotypes among individuals, known as population variation, is influenced by several factors, including the population’s genetic structure and the environment.
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Importance of genetic diversity

  • Genetic diversity or variation is the raw material for adaptation in a species.
  • A species’ future potential for adaptation depends on the genetic diversity held in the genomes of the individuals in populations that make up the species.
    • To respond to a variety of environmental changes, a species requires genetic diversity in its population.
  • A species with the greatest potential for subsequent evolution is the most genetically diverse one.
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Example - antibiotic resistance

  • Applying antibiotics to a population of bacteria will select a population of bacteria that are resistant to antibiotics.
    • The resistance comes from a gene, which would have arisen as a result of random genetic mutation.
  • The antibiotic strongly selects for this resistant gene.
  • If all the bacteria in a population were genetically identical, they would all be killed by the antibiotic.
    • This is why genetic diversity is vital for the evolution & survival of a species.
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Different environments

  • An allele that is beneficial in one environment, may be harmful in a different environment due to conflicting selection pressures.
  • A classic example of this is the evolution of the peppered moth in eighteenth- and nineteenth-century England.
    • This is covered on the subsequent slide.
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Peppered moths

  • Prior to the Industrial Revolution, the moths were predominately light in color.
  • This allowed them to blend in with the light-colored trees and lichens in their environment.
    • But, when soot began spewing from factories, the trees became darkened.
    • This made the light-colored moths easier for predatory birds to spot.
  • Over time, the frequency of the melanic form of the moth increased because they had a higher survival rate in habitats affected by air pollution because their darker coloration blended with the sooty trees.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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