This Wikipedia article states that Segue 1 is either a dwarf spheroidal galaxy or globular cluster associated with our own Milky Way. I am wondering what the difference is between dwarf spheroidal galaxies and globular clusters, since at first glance is seems that the morphological properties and stellar ages are similar between the two classes of objects.
There are many differences starting from size to the dark matter content... Please check the following link it has given much information : http://www.answers.com/topic/dwarf-spheroidal-galaxy
The main difference is if it is gravitationally bound to another galaxy or not.
A globullar cluster is a group of old stars inside a galaxy. It is not independent.
A galaxy is a group of stars, and a dwarf sheroidal galaxy is a group of (mainly) old stars, gravitationally bound in itself, but not bound inside a larger body (even when it can be orbiting a local group center of mass).
If Segue 1 is orbiting around Milky Way's center, it is a globullar cluster. If it is orbiting with Milky way about Local Group's center near Andromeda, then it is a dwarf spheroidal galaxy.