  Abridge. We have conducted a spectrophotometric study of dwarf early-type
galaxies (dEs) in the Virgo cluster and in regions of lower density. We have
found that these galaxies show many properties in common with late-type
galaxies but not with more massive early-types (E/S0). The properties of the
dEs in Virgo show gradients within the cluster. dEs in the outer parts of the
Virgo cluster are kinematically supported by rotation, while those in the
center are supported by the random motions of their stars (i.e. pressure
supported). The rotationally supported dEs have disky isophotes and faint
underlying spiral/irregular substructures, they also show younger ages than
those pressure supported, which have boxy isophotes and are smooth and regular,
without any substructure. We compare the position of these dEs with massive
early-type galaxies in the Faber-Jackson and Fundamental Plane relations, and
we find that, although there is no difference between the position of
rotationally and pressure supported dEs, both deviate from the relations of
massive early-type galaxies in the direction of dwarf spheroidal systems
(dSphs). We have used their offset with respect to the Fundamental Plane of
E/S0 galaxies to estimate their dark matter fraction. All the properties
studied in this work agree with a ram pressure stripping scenario, where
late-type galaxies infall into the cluster, their interaction with the
intergalactic medium blows away their gas and, as a result, they are quenched
in a small amount of time. However, those dEs in the center of the cluster seem
to have been fully transformed leaving no trace of their possible spiral
origin, thus, if that is the case, they must have experienced a more violent
mechanism in combination with ram pressure stripping.
