Key ideas relating to speciation, how different species occur and some links to natural selection and variation causing allele frequency to change and create new species.

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  • Speciation: formation of new species
    • Variation
      • mutation
        • point mutation: single gene is changed either by deletion, addition or inversion. e.g: Sickle celled anaemia
        • Chromosomal Mutation: changes in whole genes. e.g Downs Syndrome
      • Random fusion of gametes
      • Chiasmata: breaking and crossing over of homologous pairs of chromosomes, produces chromosomes with a new mix of genes
    • Natural selection: causes species with advantageous alleles to successfully breed, survive and pass on these alleles, this changes the allele frequency= leads to EVOLUTION
      • May happen due to selection pressure: changes in environment/conditions
        • Disruptive Selection: middle values die out
        • Directional Selection:: One extreme dies out
        • Stabilising Selection: 2 opposite ends of extremes die out
      • Less advantageous species die out
      • May happen due to competition
        • INTERSPECIFIC competition: arises between different species. e.g: food and shleter
        • INTRASPECIFIC competition occurs between the same species: e.g:mating
    • Reproductive Isolation: (for example due to behavioural patterns) leads to sympatric speciation
    • Geographical Isolation: leads to allopatric speciation
  • Geographical Isolation: leads to allopatric speciation




thank you so very much!! 

really helpful :)

Noshin Mahmud


you're welcome Laura :)

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