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  • Created by: Megan
  • Created on: 08-03-14 14:22

Types and Vocabulary

  • Species - a group of similar organisms that can reproduce and produce fertile offspring
  • Speciation - the development of a new species

Geographical Isolation (Allopatric Speciation)

  • A physical barrier divides the population
  • Two different environments
  • Natural selection and genetic drift changes the genotype and phenotype
  • Two populations evolve separately
  • They become reproductively isolated therefore becoming two distinct species

Reproductive Isolation (Sympatric Speciation)

  • A reproductive isolation occurs because changes in the alleles and phenotype of the two populations prevent them from successfully breeding together - Genetic drift can cause further divergence between isolated gene pools
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Reasons for its Occurance

  • Seasonal Changes:- individuals develop different mating or flowering seasons or become sexually active at different times of the year
  • Mechanical Changes:- changes in genetalia prevent successful mating
  • Behavioural Changes:- a group develops a different courtship ritual that is not attractive to the rest of the population
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Reproductive Isolation Mechanisms


  • Habitat Isolation - populations inhabit different local habitants within one environment
  • Temporal Isolation - same environment but are reproductively active at different times
  • Behavioural Isolation - two populations have different courtship patterns
  • Geographical Separation - populations inhabit different continents or islands etc


  • Gametes Mortality - sperm cannot reach or fertlise the egg
  • Zygote Mortality - fertilisation occurs, but the zygote fails to develop
  • Hybrid Sterility - hydrid survives (viable) but is sterile and cannot reproduce (no meiosis)
  • Hybrid Inviability - F1 hybrid has reduced viability -> incomplete development
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