  We show that ultraviolet radiation, with wavelengths shorter than 2000 A,
escaping from the disks of giant spirals could be one of the principal factors
affecting the evolution of low mass satellite galaxies. We demonstrate, using a
semi-qualitative model, that the Lyman continuum part of the radiation field
can lead to ionization of the ISM of the dwarf galaxies through the process of
photoevaporation, making the ISM virtually unobservable. The FUV part (912 <
lambda < 2000 A) is shown to dominate over the internal sources of radiation
for most of the Galactic dwarf spheroidals. The proposed environmental factor
could be at least partially responsible for the bifurcation of the low mass
proto-galaxies into two sequences - dwarf irregulars and dwarf spheroidals. We
discuss many peculiarities of the Local Group early-type dwarfs which can be
accounted for by the impact of the UV radiation from the host spiral galaxy
(Milky Way or M31).
