The image below shows a Sanger DNA sequencing gel where one ingredient was left out of all sequencing reactions. The top of the gel is the anode and the bottom of the gel is the cathode. The gel was turned on and ran correctly. What is the MOST likely missing ingredient? 
Definitions:
Analyze
The process of examining something methodically to understand its components, meaning, or relationships.
Bloom's Taxonomy
A classification system used in education to define and distinguish different levels of human cognition - i.e., thinking, learning, and understanding.
Evaluate
The process of assessing or judging the value, nature, or importance of something.
Bloom's Taxonomy
A classification system used to define and distinguish different levels of human cognition—i.e., thinking, learning, and understanding.
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