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7.3Natural Selection

Artificial Selection — AP BIOLOGY Revision Notes & Topical Questions

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Lesson summary

7.3 Artificial Selection — AP BIOLOGY notes: Explain how humans can affect diversity within a population through artificial selection.Artificial selection (selective breeding) = humans choose individuals with desired heritable traits to breed, changing the population over generat…

  • Similarity
  • Similar pressures
  • Maize and sorghum
  • Cows, sheep and goats
  • Fitness in the wild
  • Vulnerability

Section 1 of 8What artificial selection is

What artificial selection is
Artificial selection (selective breeding)
Artificial selection (selective breeding) humans choose individuals with desired heritable traits to breed, changing the population over generations.
Agent
  • Agent humans are the selective agent; in natural selection it is the environment.
Similarity
  • Similarity both need heritable variation and change allele frequencies.

Section 2 of 8Process and examples

1
Individuals with desirable traits are chosen.
2
These individuals are bred together.
3
Offspring with the desirable traits are chosen and bred together.
4
This repeats over many generations until the desired characteristic is more frequent.
1Speed
  • Speed selection is intense and targeted, so large changes occur in relatively few generations.
2Examples
  • Examples dog breeds from wolves; cabbage, broccoli, kale, cauliflower and Brussels sprouts from wild mustard; high-yield maize from teosinte; high-yield dairy cattle, faster racehorses and disease-resistant crops.
    • (Brassica oleracea)
3Aims
  • Aims enhance one trait or combine several.
    • (high yield, disease resistance and growth in poor soil)

Section 3 of 8Artificial selection and convergent evolution

Similar pressures
  • Similar pressures humans apply similar selection for agricultural efficiency, so unrelated species develop similar traits.
Maize and sorghum
  • Maize and sorghum high yield and drought resistance, with larger fruit and vibrant colour.
Cows, sheep and goats
  • Cows, sheep and goats selection for milk gave larger udders and higher metabolic efficiency independently.

Section 4 of 8Consequences

1Fitness in the wild
  • Fitness in the wild selected traits are useful to humans and may reduce fitness there.
    • (breathing problems in short-nosed dogs)
2Diversity
  • Diversity artificial selection reduces genetic diversity and can increase inbreeding, raising homozygous harmful recessives.
3Vulnerability
  • Vulnerability low diversity makes crops and livestock susceptible to disease and environmental change, e.g. the Irish potato famine.
4Evidence
  • Darwin used pigeon breeding to show selection can cause large changes, supporting the mechanism of natural selection.

Section 5 of 8Artificial and natural selection compared

FeatureArtificialNatural
Who selectsHumansEnvironment
GoalUseful traitsSurvival and reproduction
SpeedFastUsually slow
VariationOften reducedMaintained
ExampleDog breeds, cropsFinches, moths

Section 6 of 8More from the specification

Evolution
  • Change in adaptive features of a population over time through natural selection.
Malaria
  • A disease caused by Plasmodium and spread by mosquitoes.
Convergent evolution
  • Similar adaptations arising in different species from shared pressures.
Phenotypic variation
  • Differences in phenotype between organisms of the same species.

Section 7 of 8Key terms

TermMeaning
Artificial selectionhumans choosing which individuals breed
Selective breedinganother name for artificial selection
Inbreedingmating between close relatives
Genetic diversityvariety of alleles in a population
Monoculturea crop of one genetic type
Convergent evolutionsimilar traits evolving in unrelated species

Section 8 of 8Exam technique

Avoid these mistakes
Saying artificial selection creates new alleles — it selects existing variation.
Saying it increases diversity — it usually reduces it.
Treating it as unrelated to natural selection — both change allele frequencies.

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