- This allows for the comparison of whole DNA molecules rather than short sequences.
- DNA sample is taken from one species and radioactively labelled.
- DNA sample is taken from another species.
- These are mixed.
- The mixture is heated to break the hydrogen bonds holding the two DNA strands in the double helix.
- Some of the strands are partially complementary and new hydrogen bonds reform between them.
- The hybrid strands are identified because they have 50% of the radioactivity.
- The are separated from the mixture.
- Heat is then used to separate the strands.
- The temperature at which the two strands separate is measured.
- The more closely related tow species:
- The greater the number of similarities between the two species DNA;
- The greater the number of complementary base pairs form;
- The higher the number of hydrogen bonds;
- The greater the heat required to separate them.
Comparison of amino acid sequences
- When it comes to IBDP Biology, the primary structures of proteins are genetically determined.
- The degree of similarity in the amino acid sequences of the proteins reflects the genealogy between two species.
- For example, one of the most studied amino-acid sequences was that of cytochrome c.
- This is an ancient protein common to all aerobic organisms.
- The more differences in the amino acid sequence of the protein, the more distantly related the species.
- The amino acid sequence of human cytochrome c is identical to that of the chimpanzee, but differs from the dog's by 13 amino acids, and from the tuna by 31 amino acids.
- The sequence of amino acids can be compared with sequences of the protein from other species.
- From the degree of similarity between species, phylogenetic trees can be hypothesized.
- Albumins and antibodies are both proteins.
- Antibodies produced by the immune system are very sensitive to differences in the structure of molecules they are exposed to.
- The antibodies of one species will react when exposed to blood serum, containing the proteins, of another.
- A range of antibodies will be created that respond to the antigenic binding sites on the albumin.
- Albumin from one of the species being investigated is injected into another ‘outgroup’ species.
- When it comes to IBDP Biology, the antibodies that respond against albumin, are collected from this outgroup species.
- These antibodies, in the form of an antiserum are then exposed to the blood proteins of each of the other species under investigation.
- The reaction is quantified by measuring the mass of the precipitate formed.
- If an organism is very distantly related to outgroup species a strong reaction will take place between the blood serum.
- Species more closely related to the outgroup will exhibit a weaker reaction.
- This procedure is used less frequently today, due to the advancement of the other molecular methodologies.
That's the end of this topic.