Which of the following is detected by a Western Blot?

The correct choice focuses on the ability of a Western Blot to detect the presence and quantify proteins in a sample. This technique involves the separation of proteins based on their size through gel electrophoresis, followed by the transfer of these proteins to a membrane. Specific antibodies are then used to bind to the target proteins, allowing for their visualization and quantification. This makes Western Blotting a powerful tool in various applications, such as confirming the presence of specific proteins associated with diseases or measuring the levels of proteins in different conditions.

The other options do not align with the primary function of Western Blotting. DNA sequences, for instance, are typically analyzed using techniques like PCR or DNA sequencing rather than a protein-focused method like Western Blot. RNA levels are measured through methods such as Northern Blotting or quantitative PCR, which specifically target nucleic acids rather than proteins. Lastly, gene polymorphisms are generally assessed through genotyping methods, which also do not involve protein analysis. Thus, the emphasis on protein detection and quantification distinguishes Western Blot from these other molecular techniques.