Hello, I have been facing fragmentation problems with my Schizosacchoromyces pombe yeast samples that I need to use for ChIP assay.I add lysis buffer and glass beads to the pellet followed by vortexing ,storage at -80 and sonicate it next day. I always keep my samples on ice while sonication and check the probe level.When I check the fragmentation on gel, I don't see a proper fragmentation even after 35 cycles at 40% amp.