I meant that Ubuntu is still built on top of GNOME 3, using a different graphical shell called Unity, much as Mint will also be built on top of GNOME 3 using Ci

I meant that Ubuntu is still built on top of GNOME 3, using a different graphical shell called Unity, much as Mint will also be built on top of GNOME 3 using Cinnamon as the graphical shell. I wasn't implying that Unity was a fork of Gnome Shell.