For example, (arbitrary data used) if we took heamaglobin from a gorilla and a human and looked at the amino acids and they looked like this:
Human: Ser; Val; Ser; Glu; Ile; Gln; Leu; Met; His; Asn
Gorilla: Ser; Val; Val; Ser; Ile; Gln Leu; Met; His; Asn
then we could see they are relatively genetically similar with 7/10 amino acids are the same.
One way to compare proteins is by comparing antigens on the body cells of a specie. This is immunological comparison:
- Extract blood serum from a species
- Put it in a second species
- This species will produce antibodies that are complimentary to the antigens of the first species
- Extract the antibodies
- Mix them with the blood serum of a third species
- A precipitate will form if the antibodies respond to the antigens of that specie
If the antibodies that were created for the antigens of the first specie can respond to antigens of the third then that means it must be complimentary to both. That means that both antigens had a similar tertiary structure, which means they had a similar primary structure, which means they had a similar sequence of amino acids which means that had a similar base sequence which means they are genetically similar. Therefore antibody can respond to both= more precipitate= more genetically similar.
If there is not very much precipitate its because the antibody can respond to the antigens in the third species because it is not sufficiently similar to the first, this shows us that they are genetically dissimilar.
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