AQA Human Biology - Human Impact on Evolution (Unit 5, Topic 8)

These have been made to match up with the notes I've written which have the same title. They are a basic, condensed version of the notes.

Includes, Alleles & Variation, Selection, Formation of New Species and Human Impact on Selection

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Alleles & Variation

Mutation = change to quantity or structure of an organism's DNA eg. base sequence

Alleles = different forms of the same gene 

Phenotype = characteristics resulting from alleles

Phenotypic variation = total variation in characteristics of an organism caused by genetic and environmental factors

  • Genetic factors (Genotypic variation) = crossover/random assortment during meiosis, random fertilisation
  • Environmental factors = selection pressures

Mutations in gametes may be passed into offspring causing a change in phenotype, may give them a selective advantage.

Selective advantage --> more likely to survive --> reproduce --> pass on genes --> allele frequency increases

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Intraspecific competition = competition between organisms of the same species

Selection pressure = environmental forces on a population altering allele frequencies

Selective advantage = those who are best adapted to selection pressures

Natural selection = those with selective advantage reproduce and pass on successful alleles

Antibiotics act as selection pressure to bacteria. Those with highest resistance survive and reproduce.

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Isolation & Formation of New Species

Species = group of similar organisms that can produce fertile offspring

Speciation = evolution of new speies from an existing one

Reproductive isolation = groups of the same species become isolated so cannot interbreed, preventing gene flow

Reproductive isolation --> different selection pressures --> changes in allele frequencies --> formation of new species 

Allopatric speciation = geographic isolation

Sympatric speciation = prezygotic mechanisms or postzygotic mechanisms

  • Prezygotic = ecological (habitats), temporal (breeding seasons), behavioural (courtship), mechanical (anatomy), gametic (biochemical incompatability)
  • Postzygotic = hybrid sterility, hybrid invaivility (fatal abnormalities in early growth), hybrid breakdown (second generation sterile or don't develop)
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Human Activity and Selection

Human activity alters selection pressures

Humans use selective breeding to breed plants/crops or animals for specific purposes.

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