9.2 Applications
Problem
Solution
Perpendicular DGGE
Only a single band is seen
Mix normal and mutant DNA samples prior
to loading well
Difficult to visualize hetero-
1. Increase amount of DNA (1–3 µg).
duplex and homoduplex
2. Use SYBR Green I dye agent (Molecular
DNA bands
Probes, Inc.).
Unknown faint bands
Impurity or non-specificity of PCR product
Poor gradient
Insure that gradient delivery system is
working properly. See instructions
“S” curve appears to be shifted/cut
1. Increase upper gradient concentrations.
2. Level tilt rod after gel is cast.
Smear at top of gel
Probably genomic DNA. This is OK
Parallel DGGE
Normal and mutant
1. Increase or decrease run time (time course
DNA unresolved
run recommended).
2. Recalculate gradient range from perpen-
dicular gel or run a time course gel.
Air bubbles in gel
Clean glass plates
Fuzzy DNA bands
Clean wells before use. Check for matching
comb and spacer thickness.
2. Let gel polymerize for at least 60 minutes.
Bands did not migrate far
1. Increase run time.
enough into gel
2. Decrease acrylamide concentration.
3. Decrease denaturant concentration.
DNA leaks between wells
1. Acrylamide not polymerized. Add more
TEMED and ammonium persulfate to final
concentration of 0.1%.
2. Degas acrylamide solution before casting
gel.
3. Let gel polymerize for at least 60 minutes.
4. Do not overload sample well. Reduce
sample volume.
Skewed or distorted bands,
1. Impurities in acrylamide. Filter before use.
or DNA spikes in gel
Check shelf life date of acrylamide.
2. Carefully load DNA into wells. Do not
pierce or puncture wells.
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