I have tried amplifying FMR1 using forward, reverse and the chimeric primer . I see a band for 118 repeats.

But i don't see any amplification happening for full mutation (645 repeats) and pre mutation (20/193).

I have used betaine 2M for the reaction. Tried varying the concentration.But i did not work.

Any suggestion on how to amplify the full mutation allele?

Please help