M4:S3 Classification and evolution

• For hundreds of years people have been putting organisms into groups to make it easier to recognise and name them
• Classification


  The act of arranging organisms into groups based on their similarities and differences
• Taxonomy is the study of classification
• Levels of groups used in classification (taxonomic hierarchy)

  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Taxonomic hierarchy


  • As you move down the hierarchy, there are more groups at each level but fewer organisms in each group
  • The hierarchy ends with species - the groups that contain only one type of organism
• Five kingdoms


  • Prokaryotae
  • Protoctista
  • Fungi
  • Plantae
  • Animalia
• Binomial naming system


  All organisms are given one internationally accepted scientific name in Latin that has two parts - the genus name (capitalized) and the species name (lowercase)
• Names are always written in italics (or underlined if handwritten)
• Phylogeny


  The study of the evolutionary history of groups of organisms
• Phylogeny tells us who's related to whom and how closely related they are
• All organisms have evolved from shared common ancestors
• Phylogenetic tree


  Shows the relationship between members of a group and their evolutionary history
• Phylogenetic species concept


  A species is the smallest group that shares a common ancestor
• Closely related species diverged away from each other most recently
• Classification systems now take into account phylogeny when arranging organisms into groups</b>
• Early classification systems only used observable features to place organisms into groups
• Classification systems are now based on observable features along with other evidence like molecular, embryological, anatomical, and behavioural evidence
• New technologies can result in new discoveries and the relationships between organisms being clarified
• The five kingdom classification system has been replaced by the three domain system
• Domains


  Large superkingdoms that are above the kingdoms in the taxonomic hierarchy
• Molecular evidence led to the proposal of the three domain system
• Archaea and Bacteria were reclassified into separate domains due to molecular evidence showing large differences between them
• Most scientists now agree that Archaea are more closely related to Eukarya than Bacteria
• Variation


  The differences that exist between individuals
• Intraspecific variation


  Variation within a species
• Interspecific variation


  Variation between different species
• Prokaryote


  A type of single-celled organism that lacks a membrane-bound nucleus
• Archaeon


  A type of single-celled organism that is genetically distinct from bacteria and eukaryotes
• The three domain system was proposed to replace an earlier classification system
• Variation is the differences that exist between individuals
• Intraspecific variation in European robins

  • Weight range of 16-22g
  • Variation in length, wingspan, colour, beak size
• Interspecific variation in birds

  • Lightest species is the bee hummingbird at 1.6g
  • Heaviest species is the ostrich at up to 160kg
• Continuous variation


  Individuals in a population vary within a range, with no distinct categories
• Discontinuous variation


  Individuals fall into two or more distinct categories, with no intermediates
• Discontinuous variation


  • Human blood group
  • Courgette colour
  • Pea seed shape
  • Bacterial antibiotic resistance
• Causes of variation


  • Genetic factors
  • Environmental factors
  • Combination of both
• Genotype


  The genes and alleles an organism has
• Phenotype


  The characteristics displayed by an organism
• Variation caused by genetic factors

  • Blood group in humans
  • Antibiotic resistance in bacteria
• Variation caused by environmental factors

  • Accents
  • Pierced ears