classification using DNA or proteins

• clarifying evolutionary relationships:

  new or improved technologies can result in new discoveries being made and the relationships between organisms being clarified - can lead to classification systems being updated
• Technologies that have been useful for clarifying evolutionary relationships:

  • genome sequencing
  • comparing amino acid sequence
  • immunological comparisons
• Genome sequencing

  advances in genome sequencing have meant that the entire base sequence of an organims's DNA can be determined
• The DNA base sequence of one organism can then be compared to he DNA base sequence of another to see how closely related they are

  e.g. closely related species will have a higher percentage of similarity in their DNA base sequence

  e.g. humans and chimps share around 94% and humans and mice about 86%
• Genome sequencing has clarified the relationship between skunks and members of the Mustelidae family (e.g. weasels and badgers)

  Skunks were classified in the Mustelidae family until their DNA sequence was revealed to be significantly different to other members of that family - reclassified into family Mephitidae
• Comparing amino acid sequence - proteins are made from amino acids. The sequence of amino acids in a protein is coded for by the base sequence of DNA. Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins
• Cytochrome C is a short protein found in many species. The more similar the amino acid sequence of Cytochrome C in two different species, the more closely related the species are likely to be
• Immunological comparisons: similar proteins will also bind to the same antibodies
• If antibodies to a human version of a protein are added to isolated samples from some other species, any protein that is like the human version will also be recognised (bound) by that antibody
• Proteins that bind antibodies will often form a precipitate (solid mass) in solution. The more antibodies the protein binds, the more precipitate will form - so the amount of precipitate can be used to determine how similar two proteins are