  Using a 1 to 2 transition as an analytically tractable model, we discuss in
detail magneto-optical resonances of both EIA (electromagnetically induced
absorption) and EIT (electromagnetically induced transparency) types in the
Hanle configuration. The analysis is made for arbitrary rate of depolarizing
collisions in the excited state and arbitrary elliptical field polarization.
The obtained results clearly show that the main reason for the EIA sub-natural
resonance is the spontaneous transfer of anisotropy from the excited level to
the ground one. In the EIA case we predict the negative structures in the
absortpion resonance at large field detuning. The role of the finite atom-light
interaction time is briefly discussed. In addition we study non-trivial
peculiarities of the resonance lineshape related to the velocity spread in a
gas.
