My lab is trying to detect low levels of mycoplasma contamination in cell cultures. We tried gel end point PCR and primers and cycling conditions worked very well. When we used same primers and conditions in rt-pcr using sybr green, we observed bimodal dissociation curve (small peak at 79 deg and big peak at 82 deg). Primer dimer peaks are found at low level of conatmination at 75 deg. When we ran the product on gel, only one band is observed. We have been using ABI sybr green mix but when used quantitech from qiagen, 79 deg peak did not show up. I was wondering if someone can explain why there is a peak at 79 deg? Could it be allele variant? If so, then why does it not show up with Quantitech sybr green? Please see the attached picture with ABI reagent.