Influence of removing chemical gradients at lq_core, lq_env, and lq_diff on a 4G model having M_* = 0.47 M_⊙, lq_core = −0.25, lq_env = −2, and X(He)_core = 0.9. Left panels show the logarithm of the square of the Brunt-Väisälä frequency (log N², blue) and the logarithm of the square of the Lamb frequency for ℓ = 1 (log L₁², green) between log(q) = 0 and −5, for the reference model (left panel, first row), when lq_diff is removed (left panel, second row), when lq_env is removed (left panel, third row), and when lq_core is removed (left panel, fourth row). The red dotted vertical line is the lq_core (core-mantle) transition, the orange dotted vertical line is the lq_env (mantle-envelope) transition, and the black dotted line is the lq_diff (envelope of H+He/envelope of pure H) transition. Red horizontal lines are the log(σ²) of each mode and red dots indicate the radial node positions in log(q). Right panels show the pulsation spectrum associated to the models of the left panels, presented as the reduced period spacing ($\mathrm{\Delta }\mathrm{\Pi }=\mathrm{\Delta }P\times \sqrt{\ell (\ell +1)}$) as a function of the reduced period ($P\times \sqrt{\ell (\ell +1)}$).