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Thursday 3rd November 2011
How DNA Profiling Works.
Genes are exons. Exons are expressed coding sections of DNA.
Introns are the non-coding regions.
When looking at DNA we look at the introns.
Locus- the place you find a gene.
Introns are lengths of DNA between exons.
Introns have series of repeated base sequences.
The introns have varying numbers of repeated bases i.e. they are different lengths.
In the introns, these repeats are called the STR
To use introns to establish identity:
Take a DNA swab
Use restriction endonucleases to cut the DNA at known places
The resulting fragments will be different lengths.
You can then use the PCR to make more copies
During the Polymerase Chain Reaction:
First the DNA is heated to 95, so the DNA separates.
Then it is heated to 55 here the primers attach to the start of the short tandem repeat
Then to 70, this is when the polymerase attaches. Nucleotides are added, extending the
DNA from the primer. The STR repeated sequence and DNA adjacent is repeated.
This is then repeated a lot of times!!!!
DNA profiling procedure:
1) DNA is cut into fragments by restriction enzymes.
2) Double stranded DNA are loaded into the wells of an agarose gel in a tank using a
3) Negatively charged DNA moves to the positively charged electrode, so the DNA splits into
4) DNA is transferred onto a nylon membrane, by solution drawn up by the gel. DNA strands
split and stick to the membrane
5) Membrane placed in a bag with DNA probe. DNA probes forms complementary base pairs
with the single stranded DNA.
6) IF probe is radioactive, then an xray film is used to detect the fragments, if fluorescent
then a UV light is used.