We present the star formation histories (SFHs) as a function of galactocentric radius of four isolated dwarf galaxies, Cetus, Tucana, LGS-3, and Phoenix. Our results suggest that beyond some distance from the center, there are no significative differences in fundamental properties of these galaxies. In the innermost regions, dwarf galaxies appear to have formed stars during time intervals which duration varies from galaxy to galaxy. This extended star formation produces the dichotomy between dwarf spheroidal (dSph) and dwarf Transition (dTr) galaxy types. This behavior is compatible with a scenario in which global reionization stops the star formation in the outer galaxy regions and self-shielding allows extended star formation in the inner regions.