\begin{psmatrix}[rowsep=1,colsep=1.3]
  % Nodes
&  \gena &       & \genb &       & \genf &       & \gene & \\[0cm]
&        &       &       &       &       &       &       & \\[0cm]
&        &       &       &       &       & \gend &       & \\[0cm]
&  \genh &       &       &       &       &       &       & \\[0cm]
&        &       & \geng &       & \genc &       &       & \\[0cm]
&  \geni &       &       &       &       &       &       &
  % Links
  \everypsbox{\scriptstyle}
  \psset{arrows=->,nodesep=2mm,border=3pt}