diff --git a/src/microbe.py b/src/microbe.py
index 4a977e0..194b8b9 100644
--- a/src/microbe.py
+++ b/src/microbe.py
@@ -420,15 +420,16 @@ def microbe_uptake_gene(self, ReqEnz, EnzGenes, MonomersProduced):
 
         # Give each taxon a random number of additional uptake genes between the number they have and n_upgenes
         for i in range(self.n_taxa):
-            n_zero = sum(UptakeGenes.iloc[i, :][UptakeGenes.iloc[i, :] == 0])
+            zero_index = (UptakeGenes.iloc[i, :] == 0).to_numpy()
+            n_zero = int(zero_index.sum())
             if n_zero == 0:  # has all genes
                 continue
             probability_list = [0] * n_zero
             locator = np.random.choice(
-                range(1, n_zero + 1), 1, replace=True
+                range(1, n_zero + 1),  replace=True
             )  # derive n_zero >= locater >= 1 (NOTE)
             probability_list[0 : int(locator)] = [1] * int(locator)
-            UptakeGenes.iloc[i, :][UptakeGenes.iloc[i, :] == 0] = np.random.choice(
+            UptakeGenes.iloc[i, zero_index] = np.random.choice(
                 probability_list, n_zero, replace=False
             ).astype("int8")