  We investigate the present-day photometric properties of the dwarf spheroidal
galaxies in the Local Group. From the analysis of their integrated colours, we
consider a possible link between dwarf spheroidals and giant ellipticals. From
the analysis of the V vs (B-V) plot, we search for a possible evolutionary link
between dwarf spheroidal galaxies (dSphs) and dwarf irregular galaxies (dIrrs).
By means of chemical evolution models combined with a spectro-photometric
model, we study the evolution of six Local Group dwarf spheroidal galaxies
(Carina, Draco, Sagittarius, Sculptor, Sextans and Ursa Minor). The chemical
evolution models, which adopt up-to-date nucleosynthesis from low and
intermediate mass stars as well as nucleosynthesis and energetic feedback from
supernovae type Ia and II, reproduce several observational constraints of these
galaxies, such as abundance ratios versus metallicity and the metallicity
distributions. The proposed scenario for the evolution of these galaxies is
characterised by low star formation rates and high galactic wind efficiencies.
Such a scenario allows us to predict integrated colours and magnitudes which
agree with observations. Our results strongly suggest that the first few Gyrs
of evolution, when the star formation is most active, are crucial to define the
luminosities, colours, and other photometric properties as observed today.
After the star formation epoch, the galactic wind sweeps away a large fraction
of the gas of each galaxy, which then evolves passively. Our results indicate
that it is likely that at a certain stage of their evolution, dSphs and dIrrs
presented similar photometric properties. However, after that phase, they
evolved along different paths, leading them to their currently disparate
properties.
