Evidence for Relationships Between Organisms Revision Notes

AQA as biology unit 2

evidence for relationships between organisms  

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  • Created on: 20-05-12 17:24
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Evidence for relationships between organisms
When one species gives rise to another the DNA will be similar but
mutations in the bases will cause it to change
A way to determine similarities between species is to use DNA
Depends on particular property of DNA helix
Double helix splits when heated into the two
strands when it cools they rejoin
This can be used to compare to different species
DNA from the species is extracted and purified
then cut into short pieces
DNA is labelled by radioactive marker to it then
mixed with other DNA
Mixture is heated and they separate
Mixture is cooled and they recombine with
strands with complementary bases
Some will be form from strands of different
species ­DNA Hybridisation
Hybrid strands are separated out and reheated
At each stage the degree at which they are still
joined is measured
If they are closely related they will share many
commentary bases
There will be more hydrogen bonds holding the strands
They higher temperature taken to break them apart the
closer related the species
The lower the temperature the more distantly
Classification of plants was one how they looked, if single seed of two
At kew gardens new evidence based on three genes in all plants lead to
new classification
565 species of plants that represent all know families of plants in
the world
Each plant DNA sequences of three genes determined
Sequences compared by computer analysis

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Phylogenetic tree developed bases upon DNA sequences
The tree showed how species have developed into grouped
Sequence of amino acids in proteins is determined by DNA
the more similarly amino acids are of same proteins reflects how closely
related species are
two sequences are compared
counting number of similarities or differences
immunological comparisons of proteins
proteins can be compared, antibodies will respond to specific antigens
on proteins
serum albumin from species A injected into species B
Species B produces antibodies specific to antigens
Serum is…read more


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