\begin{frame}
  \small
  
  \begin{example}
  \begin{center}
    \begin{tikzpicture}[on grid,baseline=-.5ex,node distance=20mm]
    \node (a)              {\alert<2>{$\m{a}$}};
    \node (b) [below=of a] {\alert<3>{$\m{b}$}};
    \node (c) [right=of b] {\alert<4>{$\m{c}$}};
    \node (d) [right=of c] {\alert<5>{$\m{d}$}};
    \node (e) [above=of d] {\alert<6>{$\m{e}$}};
    \draw[->] (a) edge[out=205,in=155,loop] (a);
    \draw[->] (b) -- (a);
    \draw[->] (b) to[bend left=20] (c);
    \draw[->] (c) to[bend left=20] (b);
    \draw[->] (c) to (d);
    \draw[->] (d) to (e);
    \onslide<3-> \node at (a) [yshift=5mm] {\BLUE{CR,WCR}};
    \onslide<4-> \node at (b) [yshift=-5mm] {\BLUE{WN,WCR}};
    \onslide<5-> \node at (c) [yshift=-5mm] {\BLUE{WN,WCR}};
    \onslide<6-> \node at (d) [yshift=-5mm,xshift=5mm] {\BLUE{SN,WN,CR,WCR}};
    \onslide<7-> \node at (e) [yshift=5mm] {\BLUE{SN,WN,CR,WCR}};
    \end{tikzpicture}
  \end{center}
  \end{example}
\end{frame}