works!

app.py

@@ -280,45 +280,51 @@ def plot_scatter_hist(x_gene, y_gene, mode='raw'):
   # ax.fill_betweenx([plotted_data[y_gene].min(), plotted_data[y_gene].max()],
   #                 *ax.get_xlim(), color='C0', alpha=0.01, lw=0)
 
-
-def create_correct_gene_plot(genes, mode):
-  if len(genes) == 0:
-    raise gr.Error("Please select at least one gene to plot.")
-  elif len(genes) == 1:
-    plot_gene(*genes)
-  elif len(genes) == 2:
-    mode = 'norm' if mode else None
-    plot_scatter_hist(*genes, mode)
-  else:
-    raise gr.Error("Cannot plot more than two genes at a time.")
-
+def plt_to_img():
   fig = plt.gcf()
   fig.canvas.draw()
-
   image = PIL.Image.frombytes(
       'RGB', fig.canvas.get_width_height(), fig.canvas.tostring_rgb())
-
   plt.close('all')
-
   return image
 
-demo = gr.Interface(
-    create_correct_gene_plot,
-    [
-        gr.Dropdown(
-            gene_table.columns.to_list(), value=["APP", "PSENEN"], multiselect=True, label="Genes", info="Select one or two genes to plot."
-        ),
-        gr.Checkbox(label="Normalize",
-                    info="Recenter and normalize the Gaussian for two genes."),
-    ],
-    "image",
-    # examples=[
-    #     [2, "cat", ["Japan", "Pakistan"], "park", ["ate", "swam"], True],
-    #     [4, "dog", ["Japan"], "zoo", ["ate", "swam"], False],
-    #     [10, "bird", ["USA", "Pakistan"], "road", ["ran"], False],
-    #     [8, "cat", ["Pakistan"], "zoo", ["ate"], True],
-    # ]
-)
+def random_gene():
+  return np.random.default_rng().choice(gene_table.columns.values)
+
+def plot_one_gene(gene):
+  if gene is None or gene == '':
+    gene = random_gene()
+  plot_gene(gene.upper())
+  return plt_to_img(), f"{gene}"
+
+def plot_two_genes(x_gene, y_gene, is_normed):
+  if x_gene is None or x_gene == '':
+    x_gene = random_gene()
+  if y_gene is None or y_gene == '':
+    y_gene = random_gene()
+  mode = 'norm' if is_normed else 'raw'
+  plot_scatter_hist(x_gene.upper(), y_gene.upper(), mode)
+  return plt_to_img(), f"{x_gene} vs. {y_gene}"
+
+def picker(only_one_gene, x_gene, y_gene, is_normed):
+  if only_one_gene:
+    return plot_one_gene(x_gene)
+  return plot_two_genes(x_gene, y_gene, is_normed)
+
+with gr.Blocks() as demo:
+  with gr.Row():
+    with gr.Column():
+      only_one_gene = gr.Checkbox(label="Only plot Gene 1", info="By default, two genes are plotted.")
+      x_gene = gr.Textbox(label='Gene 1', value='APP')
+      y_gene = gr.Textbox(label='Gene 2', value='PSENEN')
+      is_normed = gr.Checkbox(label="Normalize", info="Recenter and normalize the Gaussian for two genes.")
+      plot_button = gr.Button("Plot")
+    with gr.Column():
+      image_output = gr.Image()
+      text_output = gr.Textbox()
+
+  plot_button.click(picker, inputs=[only_one_gene, x_gene, y_gene, is_normed], outputs=[image_output,text_output])
+
 
 if __name__ == "__main__":
   demo.launch()