QUOTE (Esta @ Nov 23 2009, 08:32 PM)

Jiajia, thats why I need help, it should have worked, but has not. I have not changed the conditions.
what do you mean by manual hotstart, and is it done with the normal taq, or is it only with those labelled as hotstart? the NEB one is not hotstart.
I am carrying out selective amplification for AFLP.
By manual hotstart, I mean that you start your PCR running on the PCR machine (WITHOUT PUTTING YOUR SAMPLES INSIDE) until it reaches 95degcel (which is usually the first step), pause the machine, put your samples (which would be in PCR tubes and note that the samples will not contain any Taq polymerase at all) in the machine, and add your Taq polymerase one by one into each sample. After the taq polymerase has been added, you can let the machine run till the end. This reduces nonspecific amplification and is similar to hotstart Taq from companies where their Taq has an inhibitor that drops off at 95degcel so the PCR reaction can start. Manual hotstart is done with the normal taq, you can try that and see if it works.