metal-poor ones (like I Zw 18) contain stars at least 1 Gyr old [@mom05], and most SBDGs have several Gyrs old stellar populations. This means that SF in the past should have proceeded in dIrrs, albeit at a low intensity and long lasting, what can at best explain their chemical characteristics, like for instance the low \[$\alpha$/Fe\] ratio [@lm04]. The \[$\alpha$/Fe\] vs. \[Fe/H\] behaviour is representative of the different production phases, $\alpha$-elements from the short-living massive stars and 2/3 of iron from type Ia SNe of longer-living binary systems. If the SF duration in a galaxy is very short, type Ia SNe do not have sufficient time to enhance the ISM with Fe and most of the stars will be overabundant in \[$\alpha$/Fe\].

[lr]{} &

\[fig:KS\]

In most SBDGs large reservoirs enveloping the luminous galactic body have been detected (NGC 1569 [@sti02], NGC 1705 [@meu98], NGC 4449 [@hun98], NGC 5253 [@kob08], I Zw 18 [@zee98c], II Zw 40 [@zee98b]) with clearly disturbed gas kinematics and disjunct from the galactic body. Nevertheless, in not more than two objects, NGC 1569 [@mue05] and NGC 5253 [@kob08] gas infall is proven, while for the other cases the gas kinematics obtrudes that the gas 