The quality of the DNA sample is poor.

Your supervisor commends you on your correct reply. He explains that since the positive control elicited the correct band, this probably means that there is a problem with the DNA sample from the eight mice. Dr. Demetriou asks you whether you remembered to store the sample at 4oC and you remember that you kept the samples at room temperature. This probably led to DNA degradation. Dr Demetriou reassures you that it may take some time to master this technique and that it works quite reliably once you get the hang of it. You proceed to tail-clip the mice again and repeat the DNA isolation,PCR and gel electrophoresis.