Page 69 - CB1.3 Genetic Varation sciPAD

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CB 1.3 GENETIC VARIATION
USING KNOWLEDGE OF GENETICS
Modelling The Forensic Use Of DNA Profiling
You have probably seen crime-based TV shows or movies where police (specifically forensic
scientists) have a sample of a person’s DNA and can use it to identify the criminal.
The process of Forensic DNA Analysis has multiple steps, but in all techniques, the DNA must be cut
into small pieces using ‘restriction enzymes’. Restriction enzymes are like ‘molecular scissors’ and
cut DNA at specific base sequences.
The fragments of DNA are then run through an electrophoresis gel (like the one shown opposite)
and the results are used to identify the culprit.
Crime Scene Analysis
Aim: To model the techniques used in forensic analysis of DNA.
Equipment: Scissors - sticky tape.
Method: 1. Cut out the four strands of DNA at the bottom of the page.
2. The restriction enzyme you are using cuts DNA when it encounters the base
sequence AATT and cuts between the AA and TT. Starting with the DNA from the
crime scene, cut your length of DNA into fragments.
3. Count the bases on each fragment and place each fragment of DNA into the
correct row on the gel on the following page.
4. Repeat steps 2 and 3 for each of the lengths of DNA from the suspects.
Results: Examine the gel and determine which of the suspect’s DNA matches the DNA
recovered from the crime scene.
Person responsible is Suspect .
Explain how you determined which of the suspects was responsible for the crime. 


1. Outline why restriction enzymes are referred to as ‘molecular scissors’. 


2. Which size fragments of DNA travel the greater distance in the gel? 

3. What causes the DNA fragments to move through the gel? 


G A A T T G C A G T G C A G T A A T T G C G T T C G A C A A T T C G G C T
DNA from the crime scene
DNA from Suspect 1
G C G T T C G A A T T C T T G G C A A T T G A A T T A T T A A T T C T T A
DNA from Suspect 2
G A A T T G C A G G T G C A T A A T T G T A C G C C A C A A T T C G G C G
DNA from Suspect 3
C G C A A T T C G G G A A T T T G C A T A G A A T T C G A C A A C T C G G
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