selection and evolution

• Reasons two species are now not able to breed successfully to produce fertile offspring

  • Geographical isolation/separation
  • No gene flow/interbreeding between both populations
  • Different environmental conditions/selection pressures
  • Random/different mutations
  • Different alleles selected for/gene pool/changes in allele frequency
  • Different morphological/physiological/behavioural features over time
  • Reproductive isolation occurs
• How selective breeding can be used to increase milk yield of cattle

  1. Choose/cross-breed females/cows/cattle with good/high milk yield

  2. Choose/cross-breed males/bulls with mothers/sisters/daughters with good/high milk yield

  3. Choose/cross-breed desirable offspring

  4. Continue/repeat for (several) generations

  5. Allele(s) for high milk yield/desired trait passed on

  6. Increase in frequency of good/best/high yield allele(s)

  7. Use artificial insemination/A.I.
• Disruptive selection

  • Mean/mode/median/average/intermediate selected against/not favoured/less fit/die
  • Both extremes selected for/favoured/more fit/survive/reproduce
  • Bimodal distribution
  • Diversifying selection
  • Causes/maintains polymorphism/genetic diversity
• Genetic basis of continuous variation

  • Different alleles at a single gene locus have small effects (on the phenotype)
  • Different genes may have an additive/combined effect (on the phenotype)
  • Multiple genes/polygenes
• Reasons species may become extinct

  • Environment changes
  • Climate/temperature/sea level change
  • Competition/predation/disease from new/introduced/alien invasive species
  • Species cannot adapt (fast enough)
  • Habitat degradation/loss
  • Hunting by humans/poaching/(over)fishing
• Principles of selective breeding in livestock

  1. Humans apply selection pressure

  2. Select parents that show desired characteristic

  3. Breed these parents together

  4. Select offspring with desired characteristics

  5. Breed selected offspring

  6. Repeating over many generations

  7. Some outbreeding required to avoid inbreeding depression/combining harmful recessive alleles
• Stabilising selection

  • Individuals in a population with intermediate phenotypes more likely to survive/reproduce
  • Individuals in a population with extreme phenotypes die/are selected against
  • No change in environment
• Genetic drift

  • Random/chance change in allele frequency
  • Larger influence in smaller population
• Reasons it is important to control alien invasive species

  • Compete with native species for food/same niche/light/resources
  • Feed on/predators of native species
  • Can cause extinction in native species
  • Can breed more successfully than native species
  • Often have no natural predator/grazers
  • May disrupt habitats/ecosystems/food webs/food chains
  • Cause reduction in biodiversity
  • May introduce disease
• Sympatric speciation

  • No geographical barrier/not geographically isolated
  • Behavioural isolation
  • Reproductive isolation
• Crop features that may be improved by selective breeding to increase yield

  • Mass/quantity/size
  • Disease resistance
  • Resistance to insects/pests
  • Rate of growth
  • Drought resistance
  • Resistance to herbicides
  • Resistance to flooding/wind
• How random sampling could be carried out on plant species

  1. Use of quadrats

  2. Size of quadrat

  3. Grid marked out

  4. Use of random number generator

  5. Measure species frequency

  6. Use of key or Braun Blanquet/other named scale to measure species abundance/percentage cover

  7. Repeat sampling

  8. Both sites treated the same
• Organisms have changed over time
• Aspects of the theory of evolution

  • Natural selection/selective advantage for survival/survival of the fittest
  • Long period of time
  • Variation