As biology

• 1 species gives rise to another species during evolution, DNA of new species will be similar to species that gave rise to it.
• Cause of mutation- suquence of nucleotidee bases of new species during evolution
• As time passes the DNA of new speices wil be more difference
• Result, expect species that are closely related to show similarity in their DNA base sequence than species that distantly related
• As there are millions of base sequence on each organism, DNA contain vast amount of infor about evolutionary history of each organism
• Use DNA hybridisation to find similar and differences of DNA

DH measures the degree of genetic similarity between pools of DNA sequences. It is used to determine the genetic distance between two species.

Technique

• DNA sample from 2 different species are heated separately to a boiling point in order to separate strands
• samples mixed + allowed to cool
• separate strands from 2 sample begin to hybridised, (re-bind), these are identified as they 50% labelled
• hybrid strands are separated out + temp is increases in stages
• if 2 species are closely related, they share complementary bases, hydrogen bonds link them together
• more H bonds, stronger hybrid strand will be
• stronger hybrid strand, higher temp needed to separate into 2 single strands, high temp at which hybrid strand spilts, more closely 2 species are related
• lower temp at which hybrid spilts, more distantly species are related.

• Sequence of amino acids in proteins is by DNA
• Degree of similarity in amino acids sequence of same protein in 2 species will reflect how closely 2 specis are related
• once amino acid sequence for chosen protein for 2 species, 2 sequences are compared.

• Serum from species A is injected to the species B
• Species B has got the antigen from species A
• Serum is extracted from species B, this serum contains antibodies specific to antigens from species A
• Serum from species B is mixed with serum from the blood of a 3rd species C
• Antibodies respond to their antigens of species C.
• Greater number of similar antigens, more precipitate is formed + more closely species are related.
• Fewer number of similar antigens, less precipitate is fromed, + more distantly species related.

Example:-

• Human serum injected into rabbit
• rabbit serum with anti-human antibodies
• rabbit serum added to other species.