<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def panels(self):
 """ Add 2 panels to the figure, top for signal and bottom for gene models """

        ax1 = self.fig.add_subplot(211)
        ax2 = self.fig.add_subplot(212, sharex=ax1)
        return (ax2, self.gene_panel), (ax1, self.signal_panel)