Case Of The Crown Jewels Template Page 11
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28Step 4 – Electrophorese the samples
Connect the cables and run the gels at 100 volts until the blue portion of the loading dye
migrates about 30 mm from the wells.
Step 5 – View the results of gel electrophoresis
If the blue stain EGels are used, results should be visible without a light. If ethidium bromide is
used, a UV light must be used to see the DNA bands on the gel.
Methylene blue may also be used to stain the gel. To stain manually, place the gel in a plastic
container, which is a little larger than the gel. Add enough 0.025 percent methylene blue
solution to cover the gel about one quarter of an inch. Stain the gel for 20 – 30 minutes.
Carefully pour off as much of the methylene blue solution as possible; the entire gel will appear
deep blue. Rinse the gel in running tap water. Let the gel soak covered with water for
approximately 10 minutes. Rock the tray occasionally to help destain the gel. Repeat three to
four times. The DNA bands will become more distinct as the gel destains.
Photograph or sketch the gel (gels may also be viewed on an overhead projector). Gels can be
stored in plastic zip lock bags in the refrigerator.
Step 6 - Interpretation
After staining, the pattern of DNA bands resulting from restriction analysis from one suspect
will match the crime scene, as shown in Figure 3. Results may vary. Students write their
analysis in a lab notebook with evidence to support their results. To facilitate discussion,
choose a representative gel and put it on an overhead
FIGURE 3: Restriction Analysis
projector. Highlight the bands projected on the board
of DNA Evidence
with a marker. Some sample questions could be:
Crime
Suspect
Suspect
What can be inferred from the results of the
DNA
1
2
Negative
tests?
Electrode (-)
Can you presume guilt by showing that the
bands of DNA match after restriction analysis?
Positive
Electrode (+)
Case of the Crown Jewels
Page 9
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