Variation and evolution

• Discontinuous variation is a type of variation that can be categorised, e.g., blood group. A characteristic can only appear in discrete values and is influenced by one or two genes with little effect from environmental factors
• Natural selection causes a change in allele frequencies over generations by favoring organisms with advantageous characteristics, leading to the passing of favorable alleles to offspring and a decrease in the frequency of unfavorable alleles
• Evolution is the change in allele frequencies in a gene pool of a population over time, occurring due to natural selection
• Types of variation

  • Continuous
  • Discontinuous
  • Heritable
  • Non-heritable
• Examples of selection pressures

  • Predation
  • Disease
  • Com
• Both genetic and environmental factors produce variation between individuals
• Selection pressures are environmental factors that drive evolution by natural selection and limit population sizes, changing the frequency of alleles in a population
• Continuous variation is a type of variation that cannot be categorised, e.g., height. It produces a continuous range where a characteristic can take any value and is influenced by multiple genes and significantly affected by environmental factors
• What is interspecific competition?
• How can allele frequencies be expressed?
• Genetic drift is variations in allele frequencies in small populations due to chance (rather than as a result of selection pressures)
• Intraspecific competition is a type of competition that takes place between members of the same species
• What is the Hardy-Weinberg principle?
• Allele frequencies can be expressed as a percentage or proportion of the total number of all alleles for that gene
• Interspecific competition is a type of competition that takes place between members of different species
• Gene pool


  All of the different versions of genes (alleles) in the individuals that make up a population
• What is meant by the founder effect?
• The Hardy-Weinberg principle is a model that allows the estimation of the frequency of alleles in a population, as well as whether allele frequency is changing over time
• Types of competition

  • Interspecific
  • Intraspecific
• Selection pressures

  • Predation
  • Disease
  • Competition (for food, habitats, mates)
  • Environmental conditions, e.g. temperature
• What is intraspecific competition?
• Assumptions made by the Hardy-Weinberg principle


  • No mutations occur to create new alleles
  • No migration in or out of the population
  • No selection, alleles are all equally passed on to the next generation
  • Random mating
  • Large population
• What is genetic drift?
• The founder effect is when a small number of individuals become isolated, forming a new population with a limited gene pool. Allele frequencies are not reflective of the original population
• Assumptions made by the Hardy-Weinberg principle


  • No mutations occur to create new alleles
  • No migration in or out of the population
  • No selection, alleles are all equally passed on to the next generation
  • Random mating
  • Large population
• Define speciation
• Reasons for speciation

  • Genetic drift in isolated population
  • Founder effect
  • Natural selection
• Hardy-Weinberg equation for calculating allele frequency


  The frequencies of each allele for a characteristic must add up to 1.0 giving the equation: p + q = 1.0 where p = frequency of the dominant allele, and q = frequency of the recessive allele
• Speciation is the formation of new species due to the evolution of two reproductively separated populations
• Allopatric speciation is the term for speciation that occurs when two populations become geographically isolated
• What is the term for speciation that occurs when two populations become geographically isolated?
• What are the two types of speciation?
• Outline geographical isolation
• Name the potential isolation mechanisms in sympatric speciation
• Sympatric speciation is the term for speciation that occurs when two populations within the same area become reproductively isolated
• Potential isolation mechanisms in sympatric speciation

  • Genetic drift
  • Founder effect
  • Natural selection
• Hardy-Weinberg equation for calculating genotype frequency

  The frequencies of each genotype for a characteristic must add up to 1.0 giving the equation: p2 + 2pq + q2 = 1.0 where p2 = frequency of homozygous dominant, 2pq = frequency of heterozygous, and q2 = frequency of homozygous recessive
• Geographical isolation is when a physical barrier (such as a river or mountain) separates two populations of the same species
• Assumptions made by the Hardy-Weinberg principle
• What is the term for speciation that occurs when two populations within the same area become reproductively isolated?