Topic 7 - Genetics, populations, evolution and ecosystems

• Phenotype


  The expression of the genes and its interactions with the environment
• Homozygous


  A pair of homologous chromosomes carrying the same alleles for a single gene
• Heterozygous


  A pair of homologous chromosomes carrying two different alleles for a single gene.
• Recessive allele


  An allele only expressed if no dominant allele is present
• Dominant allele


  An allele that will always be expressed in the phenotype
• Codominant


  Both alleles are equally dominant and expressed in the phenotype.
• Multiple alleles


  More than two alleles for a single gene
• Sex-linkage


  A gene whose locus is on the X chromosome
• Autosomal linkage


  Genes that are located on the same chromosome not sex chromosomes
• Epistasis


  When one gene modifies or masks the expression of a different gene at a different locus.
• Monohybrid


  Genetic inheritance cross of a characteristic determined by one gene
• Dihybrid


  Genetic inheritance cross for a characteristic determined by two genes
• Gene pool


  All the alleles of all the genes within a population at one time
• Allele frequency


  The proportion of an allele within the gene pool
• Hardy-Weinberg equations


  p2 + 2pq + q2 = 1

  p + q = 1
• Disruptive selection


  When individuals which contain the alleles coding for either extreme trait are more likely to survive and pass on their alleles
• Disruptive


  Leads to speciation
• Speciation


  Creation of new species
• Two types of speciation

  Allopatric or Sympatric
• Allopatric speciation

  Geographically isolated leading to reproductive isolation

  Population physically separate into two

  Unable to reproduce

  Accumulation of differences over time

  Unable to interbreed to create fertile offspring
• Sympatric speciation

  • Differences in behaviour leads to reproductive isolation
  • Due to random mutation e.g change in courtship ritual or fertile at different times of the year
  • Individuals will not reproduce together so no gene flow
  • Accumulate different mutations so DNA is different
  • Cannot interbreed to create fertile offspring Classified as two different species
• Genetic drift


  Change in the allele frequency within a population between generations
• Substantial genetic drift leads to


  Evolution
• Population


  Group of organisms of the same species living in the same habitat
• Habitat


  Part of an ecosystem in which particular organisms live in
• Community


  All the populations of different species in the same area at the same time
• Ecosystem


  A community and the non-living components of an environment (biotic and abiotic factors)
• Niche


  An organism’s role within an ecosystem, including their position in the food web and habitat
• Carrying capacity


  The maximum population size an ecosystem can support
• Abiotic factors


  Non-living conditions of an ecosystem
• Biotic factors


  Impact of the interactions between organisms
• Interspecific competition


  Members of different species are in competition for the same resources that is in limited supply
• Intraspecific competition


  Members of the same species are in competition for resources and a mate
• Predator-prey graphs

  • Size of the predator and prey population both fluctuate
  • Always be more prey than predators
  • Population will always change in the prey then the predators (lag time)
• Ensure that samples are representative by:

  • Random sampling removes bias
  • Large sample
  • Line transects to examine a change over a distance
• Estimate the size of a non-motile population


  Divide area into a grid

  Generate a pair of coordinates using a random number generator

  Place a quadrat her and count frequency of species

  Repeat a large number of times (>10) and calculate mean per quadrat

  Population size = (total area of habitat / quadrat area) x mean per quadrat
• Mark-release recapture

  Capture sample of species, mark and release

  Ensure marking is not harmful / doesn't affect survival

  Allow time for organisms to randomly distribute before collecting second sample

  Population size = (no. in sample 1 x no. inn sample 2) / no. marked in sample 2
• Succession


  Change in a community over time due to a change in abiotic/ species
• Primary succession

  1. Colonisation of pioneer species
  2. Pioneer species change abiotic conditions e.g. they dies and decompose
  3. Environment becomes less hostile for other species with different adaptations and less suitable for previous species, so better adapted species outcompete previous species
  4. As succession continues, biodiversity increases
  5. Climax community reached