|There is no cell pellet after centrifuging the cheek cell suspension
|Not enough cheek cells in suspension.
|Mouth must be vigorously rinsed for at least 60 seconds to harvest loose cheek cells.
|Sample not centrifuged fast enough.
|Spin cells at maximum speed (17,000 x g) for 2 minutes. If your centrifuge does not reach this speed, spin at highest available speed for 4 minutes.
|I was not able to extract DNA from hair
|Not enough hairs used for extraction.
|Use at least five hairs for DNA extraction.
|No follicle was present on hair shaft.
|The best place to collect hairs for this experiment is the head. Pick hair follicles which have a bulbous base (sheath ends).
|Poor DNA Extraction
|Samples not mixed well enough during extraction.
|In addition to flicking the tube, vortex or pipet up and down to mix the sample.
|Proteinase K inactive because it was prepared too far in advance.
|Prepare Proteinase K within one hour of use.
|Water baths not at proper temperature.
|Use a thermometer to confirm water bath set point.
|Not enough DNA
|Try cheek cell extraction. Final DNA concentrations are usually higher.
|The extracted DNA is very cloudy
|Cellular debris from pellet transferred to tube.
|Centrifuge sample again and move supernatant to a fresh tube. Take care to avoid pellet.
|Cellular debris not separated from supernatant.
|Centrifuge sample again. If possible, centrifuge at a higher speed. Move cleared supernatant to a fresh tube.
|After staining, the ladder and control PCR products are visible on gel, but some student samples are not present
|Student DNA sample was not concentrated enough.
|Poor DNA extraction. Extract new DNA. Cheek cell extraction usually results in higher DNA yield.
|Student DNA sample was degraded.
|If DNA is not used immediately following extraction, store sample at -20˚C.
|Wrong volumes of DNA and primer added to PCR reaction.
|Practice using pipettes.
|Some students have more or less amplification than others
|Concentration of DNA varies by sample.
|There is an inherent variability in the extraction process. For best results, use cheek cell extraction.
|Low molecular weight band in PCR samples
|Low concentration of extracted DNA in PCR reaction.