The main Gnome edition forked off Ubuntu with Barbara which was based on Edgy.
All the versions of the main edition is based on the previous version. Clem uses programming tools and "handicraft" to tweak Mint after the new Ubuntu and of course adds a taste of Mint - the Mint tools and the art work.
This means that it is not exactly the same as the equivalent Ubuntu version, Mint tends to be less buggy and mostly wifi works better. There may also be deliberate differences like in printing where Daryna kept it as in Celena while Gutsy is different from Feisty.
The other important edition is the KDE edition. It is based on Gutsy Kubuntu with the Mint tools (that are gnome) ported to KDE. To make the Mint tools work in KDE was a major undertaking.
The KDE edition will continue to be based on the previous version like the main edition, but here it is Boo that is "tweaking"