How could your cells be optimized for Gibco FBS – unless you have been using the same lot all these years?  Every time the lot changes, you have a new serum.  Hundreds of different fetuses from different collection sites, go into making each new lot – - – the same as with Gemini.  Therefore every lot is a bit different from every other lot.  If you look at the specs for the serum types, Gemini’s specs for each grade of FBS is much tighter than Gibco’s – so there would be less lot to lot variations with the Gemini than with the Gibco FBS.