When organisms evolve, the molecules of which they are made adapt and change.
DNA determines proteins of organism, including enzymes and proteins determine features of an organism.
Changes in features are due to changes in DNA.
Comparison of DNA base sequences
One species gives rise to another species during evolution = DNA of new species is initially very similar to that of original species.
Sequences of nucleotide bases in the DNA of the new species will change due to mutations.
Over time new species will accumulate more differences in its DNA - species that are more closely related show more similarity in DNA base sequences than species that are more distantly related.
DNA contains a vast amound of information about the evolutionary history of all organisms.
= way of determining similarities between DNA of different organisms.
Depends upon a particular property of DNA double helix - when heated, DNA's double strand seperates into two complemenatary single strands - when cooled, strands recombine with each other to form original double strand. - with sufficient time a mixture of DNA pairs up with thier partners.
NB: DNA determines features of an organism - evidence for a close evolutionary relationship between species so provides direct record - using similarites themselves = indirect record. However some DNA isn't functional (doesn't code for proteins) - analysis of this can provide new evidence.
- DNA from two species extracted, purified and cut into short pieces.
- DNA from one of the species labelled by attaching radioactive or flourescent marker. - mixed with unlabelled DNA from other species.
- Mixture of both sets of DNA heated to separate strands.
- Mixture cooled to allow strands to combine with other strands that have complementary base sequences.