Restriction of a Specht module to the alternating group

Question

Let $n\in\mathbf{N}$ and denote by $S_n$ the symmetric group on $n$ letters. For $\lambda\vdash n$ a partition of $n$ the Specht module $S^\lambda$ defines an irreducible representation. What happens, when such a module is restricted to the alternating group $A_n$?