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Case 1 - Introduction
Before we try to solve the first case, there are a few questions listed below that could help you better understand this process. To find an answer to any of the given questions, simply click the respectable link below.
What produces the differences in a DNA fingerprint?
How do you make a DNA fingerprint?
Why do you probe the gel?
How do you make a complete DNA fingerprint?
What produces the differences in a DNA fingerprint?
Each of us has two copies of each chromosome...one from dad, and one from mom.
On each chromosome, at a placed called a Locus, there's a series of represented DNA units. One repeat is called a "core sequence" and could have from 9 to 35 DNA bases (A,T,C or G).
The difference between one fingerprint and another is the number of these core sequences next to each other as tandem repeats.
This differences produces the variable number of tandem repeats (VNTR) in a DNA fingerprint.
How do you make a DNA fingerprint?
A restriction enzyme cuts out the tandem repeats in the initial step of a DNA fingerprint.
The pieces of DNA, cut off by restriction enzymes, are placed in a gel along with millions of other pieces of DNA, cut up by the restriction enzyme.
When an electric potential is created in the gel, the negative DNA fragments migrate towards the positively charged anode.
The result is a continuous line of DNA, with the shortest pieces migrating further than the longer pieces.
The trick is how do you find the two pieces of DNA containing the core sequences? Easy, use a probe that is the mirror image of core sequences in each VNTR. So...a core sequence of AATTCCAGC requires a probe with TTAAGGTCG!
Why do you probe the gel?
The probe is radioactive, so it can be developed as a shadow on an xray film!
How do you make a complete DNA fingerprint?
Use five separate probes and develop five xray images. An innocent person may match one fingerprint with suspect DNA, but it is incredibly unlikely that he/she would match all five.
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