species/taxonomy

• what are species?

  A group of organisms that can interbreed and produce fertile offspring
• historical classification was based on observable characteristics

  now new technologies are used to make genetic comparisons
• organisms placed in 8 different groups called taxa/a taxon
• taxa are arranged in a hierarchy
• what is heirachy?

  1. large groups divided into smaller groups
  2. with no overlap
• the 8 taxa:

  1. domain
  2. kingdom
  3. phylum
  4. class
  5. order
  6. family
  7. genus
  8. species
• more closely related species have:

  • more similar DNA base sequences
  • more similar amino acid sequences in proteins (when comparing same protein)
  • less mutations in base sequence -> since species diverged
• advantaged of modern gene technology:

  • directly compare DNA base sequences
  • directly investigate genetic diversity within a species (intraspecific)
  • directly investigate genetic diversity between different species (interspecific)
• more closely related -> have a more recent common ancestor
• classifying species can be difficult:

  1. unable to observe reproductive behaviour
  2. limitations of observable features
• new technologies:

  1. genome sequencing
  2. protein/amino acid comparisons
  3. immunological comparisons
• genome sequencing:

  3 types:

  • compare % similarity of DNA base sequences
  • compare base sequences for a specific gene
  • DNA hybridisation
• % similarity of DNA base sequences:

  • higher % similarity of DNA base sequences -> less mutations
  • so diverged more recently
  • so more closely related
• comparing base sequences for a specific gene:

  • more similar base sequence -> less mutations
  • so diverged more recently
  • so more closely related
• DNA hybridisation: PROCESS

  • DNA base sequences for same gene collected from two species
  • sequences heated to break hydrogen bonds and separate strands
  • both species DNA mixed together
  • hybridised DNA is separated
• DNA hybridisation: RESULTS

  • if hybridised DNA has a higher separation temperature
  • more hydrogen bonds needed to be broken to separate strands
  • so more complementary base pairs formed
  • so species are more closely related -> few/no mutations
• protein/amino acid comparisons:

  • more AA differences in sequence of two species
  • means more mutations have occurred
  • since they diverged
• genetic code is degenerate -> different base sequence can form same AA sequence
• immunological comparisons: PROCESS

  • inject organism with protein from species A
  • organism makes antibodies
  • collect blood serum containing antibodies to protein from A
  • mix serum with proteins from different species
  • compare amount of precipitate formed
• immunological comparisons: RESULTS

  • higher amount of precipitate -> protein from different species has more similar shape to antibody from A
  • so protein has more similar AA sequence
  • so more similar DNA base sequence
  • therefore is more closely related
• all eukaryotes have cytochrome c protein