Genetics

• Genetic diversity: the number of different alleles of genes in a population
• Population: all the organisms of one species living in a habitat
• Natural selection:

  1. random mutations can result in new alleles of a gene
  2. many mutations are harmful, but in certain environments the new alleles may benefit their possessor
  3. this leads to an increased chance of survival and so an increased reproductive success
  4. the advantageous allele is passed on to the next generation
  5. over many generations, the new allele will increase in frequency in the population
• Genetic bottleneck: an event that causes a big reduction in population, reducing the number of different alleles in the gene pool
• Founder effect: a small group of organisms from a population start a new colony, as a result of migration
• Adaptations:

  • behavioural: changes in behaviour
  • physiological: changes in biological processes
  • anatomical: changes in physical/structural features
• Directional selection

  • in response to an environmental change
  • acts in favour of an extreme phenotype
  • eg antibiotic resistance

  
• Stabilising selection

  • occurs in a stable environment
  • acts against extreme phenotypes and favours the norm
  • eg human birth weights

  
• Species: a group of organisms that can produce live, fertile offspring
• Courtship

  • species specific: only members of the same species will respond
  • allows them to recognise each other, preventing interbreeding and making reproduction more successful
  • helps us classify species
• A phylogenetic classification system arranges species into groups based on their evolutionary origins and relationships.
• Hierarchy:

  • smaller groups within larger groups
  • no overlap between groups
  • each group is called a taxon
• Binomial naming: Genus + species
• Binomial naming system allows species to be universally identified and avoids the confusion of using common names
• Biodiversity: the variety of living organisms in an area. Ranges from local to global diversity
• Species richness: the number of different species in a community
• Index of diversity: $d=$$N(N-1)/Σn(n-1)$
• The higher the index of diversity, the more diverse the area is.
• Woodland clearance and hedgerow removal increases the area of farmland, but destroys habitats so species lose their shelter and food source.
• Pesticides and herbicides kill pests and weeds, but organisms that feed on them will lose their food source
• Monoculture: the cultivation of a single crop in a given area
• Groups are arranged in a hierarchy:

  A) Domain

  B) Kingdom

  C) Phylum

  D) Class

  E) Order

  F) Family

  G) Genus

  H) Species

  
• Comparisons of genetic diversity

  • base sequence of DNA
  • base sequence of mRNA
  • amino acid sequence of proteins
  • comparing observable features/characteristics
• Reasons for low level of genetic diversity

  • genetic bottleneck: an event causes a reduction in population size, so only a few alleles are left
  • founder effect: a population is started with a small number of individuals
  • inbreeding
• Random sampling:

  • avoids bias
  • produces reliable/repeatable results
• Index of diversity is more useful

  • it measures the population size of each species
  • so useful as there may be many organisms of some species and few of other species
• Standardize sampling procedure:

  • same size of area sampled
  • same sample size net
  • same sampling time
  • sample taken on same time of day/same day of the week
• Representative data

  • random sampling
  • large number of samples
• Replanting hedges:

  • more plants, more food sources, more habitats
  • greater biodiversity -> increase in predators of pests
  • increase in predators of pests/pollinators -> more yield
  • attract tourists to the farm -> more income from diversification
• Replanting hedges:

  • reduces land area for crop growth
  • greater biodiversity -> more pests -> less yield
• Improving sampling method

  • collect at more times of the year -> better line of best fit
  • count the number of individuals of each species -> calculate index of diversity
  • collect from more sites/more years -> increase accuracy of mean
• Higher p-value means its more likely due to chance, so less significant
• Genetic diversity: the number of different alleles of each gene
• Sampling method

  • set up a grid system with coordinates
  • place quadrants selected at random
  • count number of organisms in each quadrat
  • repeat and calculate mean