diff --git a/change_quality.py b/change_quality.py
index 84537ee..9d5f194 100644
--- a/change_quality.py
+++ b/change_quality.py
@@ -5,29 +5,29 @@ import os
 
 
 ### FORWARD
-def generate_quality_first_bases_fw():
-    return ''.join(random.choice('?@ABCD') for _ in range(2))
+def generate_quality_first_bases_fw(read_length):
+    return ''.join(random.choice('?@ABCD') for _ in range(int(read_length * 0.02)))
 
-def generate_quality_next_bases_fw():
-    return ''.join(random.choice('ABCDEG') for _ in range(3))
+def generate_quality_next_bases_fw(read_length):
+    return ''.join(random.choice('ABCDEG') for _ in range(int(read_length * 0.02)))
 
-def generate_quality_middle_bases_fw():
-    return ''.join(random.choice('CDEFGH') for _ in range(5))
+def generate_quality_middle_bases_fw(read_length):
+    return ''.join(random.choice('FGH') for _ in range(int(read_length * 0.10)))
 
-def generate_quality_last_bases_fw():
-    return ''.join(random.choice('HI') for _ in range(200))
+def generate_quality_last_bases_fw(read_length):
+    return ''.join(random.choice('HI') for _ in range((int(read_length * 0.60))))
 
-def generate_quality_decreasing_200_220_fw():
-    return ''.join(random.choice('CDEFGH') for _ in range(30))
+def generate_quality_decreasing_200_220_fw(read_length):
+    return ''.join(random.choice('CDEFGH') for _ in range(int(read_length * 0.10)))
 
-def generate_quality_decreasing_220_260_fw():
-    return ''.join(random.choice('ABCDEG') for _ in range(25))
+def generate_quality_decreasing_220_260_fw(read_length):
+    return ''.join(random.choice('ABCDEG') for _ in range(int(read_length * 0.10)))
 
-def generate_quality_decreasing_260_290_fw():
-    return ''.join(random.choice('?@ABCD') for _ in range(25))
+def generate_quality_decreasing_260_290_fw(read_length):
+    return ''.join(random.choice('?@ABCD') for _ in range(int(read_length * 0.04)))
 
-def generate_quality_decreasing_290_300_fw():
-    return ''.join(random.choice('?@') for _ in range(10))
+def generate_quality_decreasing_290_300_fw(read_length):
+    return ''.join(random.choice('?@AB') for _ in range(int(read_length * 0.02)))
 
 def change_quality_fw(input_file, output_file):
     with open(input_file, 'r') as f_in, open(output_file, 'w') as f_out:
@@ -40,45 +40,45 @@ def change_quality_fw(input_file, output_file):
                 f_out.write(line)
             else:
                 new_quality = (
-                    generate_quality_first_bases_fw() +
-                    generate_quality_next_bases_fw() +
-                    generate_quality_middle_bases_fw() +
-                    generate_quality_last_bases_fw() +
-                    generate_quality_decreasing_200_220_fw() +
-                    generate_quality_decreasing_220_260_fw() +
-                    generate_quality_decreasing_260_290_fw() +
-                    generate_quality_decreasing_290_300_fw()
+                    generate_quality_first_bases_fw(read_length) +
+                    generate_quality_next_bases_fw(read_length) +
+                    generate_quality_middle_bases_fw(read_length) +
+                    generate_quality_last_bases_fw(read_length) +
+                    generate_quality_decreasing_200_220_fw(read_length) +
+                    generate_quality_decreasing_220_260_fw(read_length) +
+                    generate_quality_decreasing_260_290_fw(read_length) +
+                    generate_quality_decreasing_290_300_fw(read_length)
                 )
                 f_out.write(new_quality + '\n')
 
 
 ### REVERSE
 def generate_quality_first_bases_rv(read_length):
-    return ''.join(random.choice('?@ABCD') for _ in range(read_length * 0.01))
+    return ''.join(random.choice('?@ABCD') for _ in range(int(read_length * 0.01)))
 
 def generate_quality_next_bases_rv(read_length):
-    return ''.join(random.choice('ABCDEG') for _ in range(read_length * 0.02))
+    return ''.join(random.choice('ABCDEG') for _ in range(int(read_length * 0.02)))
 
 def generate_quality_middle_bases_rv(read_length):
-    return ''.join(random.choice('CDEFGH') for _ in range(read_length * 0.02))
+    return ''.join(random.choice('CDEFGH') for _ in range(int(read_length * 0.02)))
 
 def generate_quality_main_bases_rv(read_length):
-    return ''.join(random.choice('HI') for _ in range((read_length * 0.10 * 6) + (read_length * 0.05)))
+    return ''.join(random.choice('HI') for _ in range((int(read_length * 0.10) * 6) + (int(read_length * 0.05))))
 
 def generate_quality_decreasing_175_200_rv(read_length):
-    return ''.join(random.choice('CDEFGH') for _ in range(read_length * 0.10))
+    return ''.join(random.choice('CDEFGH') for _ in range(int(read_length * 0.10)))
 
 def generate_quality_decreasing_200_220_rv(read_length):
-    return ''.join(random.choice('ABCDEG') for _ in range(read_length * 0.10))
+    return ''.join(random.choice('ABCDEG') for _ in range(int(read_length * 0.10)))
 
 def generate_quality_decreasing_220_260_rv(read_length):
-    return ''.join(random.choice('?@ABCD') for _ in range(read_length * 0.05))
+    return ''.join(random.choice('?@ABCD') for _ in range(int(read_length * 0.05)))
 
 def generate_quality_decreasing_260_290_rv(read_length):
-    return ''.join(random.choice('?@ABC') for _ in range(read_length * 0.04))
+    return ''.join(random.choice('?@ABC') for _ in range(int(read_length * 0.04)))
 
 def generate_quality_decreasing_290_300_rv(read_length):
-    return ''.join(random.choice('?@AB') for _ in range(read_length * 0.01))
+    return ''.join(random.choice('?@AB') for _ in range(int(read_length * 0.01)))
 
 def change_quality_rv(input_file, output_file):
     with open(input_file, 'r') as f_in, open(output_file, 'w') as f_out:
@@ -90,16 +90,17 @@ def change_quality_rv(input_file, output_file):
             elif line_num % 4 == 2:
                 f_out.write(line)
             else:
+                read_length = len(line.strip())
                 new_quality = (
-                    generate_quality_first_bases_rv() +
-                    generate_quality_next_bases_rv() +
-                    generate_quality_middle_bases_rv() +
-                    generate_quality_main_bases_rv() +
-                    generate_quality_decreasing_175_200_rv() +
-                    generate_quality_decreasing_200_220_rv() +
-                    generate_quality_decreasing_220_260_rv() +
-                    generate_quality_decreasing_260_290_rv() +
-                    generate_quality_decreasing_290_300_rv()
+                    generate_quality_first_bases_rv(read_length) +
+                    generate_quality_next_bases_rv(read_length) +
+                    generate_quality_middle_bases_rv(read_length) +
+                    generate_quality_main_bases_rv(read_length) +
+                    generate_quality_decreasing_175_200_rv(read_length) +
+                    generate_quality_decreasing_200_220_rv(read_length) +
+                    generate_quality_decreasing_220_260_rv(read_length) +
+                    generate_quality_decreasing_260_290_rv(read_length) +
+                    generate_quality_decreasing_290_300_rv(read_length)
                 )
                 f_out.write(new_quality + '\n')