TOPIC 7 - GENETICS/POPULATIONS

• Genotype

  • the genetic constitution of an organism
• Phenotype

  • the expression of the genetic constitution
  • and its interaction with the environment
• Homozygous

  • two copies of the same allele for a gene
• Heterozygous

  • two different alleles for the same gene.
• Recessive allele

  • An allele that is only expressed if there are no dominant alleles present
• Dominant allele


  • An allele that is always expressed in the phenotype
• Codominance

  • two alleles are both dominant both are expressed in the phenotype
• Multiple alleles

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

  • a gene located on the X chromosome
  • in the non-homologous region
• Autosomal linkage


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• Epistasis

  • When one gene masks/modifies with the expression of another gene
• Monohybrid

  • The inheritance of one gene
• Dihybrid

  • The inheritance of two genes
• Natural selection

  • the process that leads to evolution in populations
  • results in species becoming better adapted to their environment
• Selection pressure

  • factors that affect the survival of an organism
  • the driving force of natural selection
• Differential reproductive success

  • not all individuals are equally likely to reproduce
  • results in changes in allele frequencies within a gene pool
• Allele frequency

  • The proportion of an allele in the population
• Disruptive selection


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• Reproductively isolated

  • Two populations of the same species, but they cannot breed together
  • there is no gene flow
• Speciation

  • the process that results in the creation of new species
• Allopatric speciation


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• Sympatric speciation

  • Two populations become reproductively isolated whilst in the same location
  • e.g. due to changes in behaviour
  • results in the formation of two new species.
• Genetic drift


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• Population

  • All the individuals of one species in the same area at the same time
• Habitat

  • The range of physical, biological and environmental factors in which a species can live
• Community

  • all the species in a particular area at a particular time
• Ecosystem

  • a community and the non-living components of an areathey can range from very small to very large in size
• Niche

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

  • The maximum population size an ecosystem can support
• Abiotic factors

  • Non-living conditions of an ecosystem
• Biotic factors

  • impact and interactions between organisms
• Interspecific competition

  • Competition between members of different species
• Intraspecific competition

  • Competition between members of the same species
• Predator-prey relationship


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• When would you use random

  sampling?

  • when there is a uniform distribution of the plant species
  • to avoid bias
• Quadrat

  • a frame
  • gridded or opened
  • used to sample non-motile organisms
• What must you do to ensure your samples are representative?

  • Take a large sample (at least 30)
  • randomly sample
• When would you use a line transect

  • When sampling a non-uniform area
  • e.g. a rocky shore
• Belt transect

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• Interrupted belt transect


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