Which reaction is used to demonstrate DNA in tissue sections?

• A. Feulgen reaction
• B. Gram stain
• C. PAS reaction
• D. Silver stain

Answer: (A)

DNA in tissue sections is demonstrated with a reaction that specifically targets the aldehyde groups formed on deoxyribose after acid hydrolysis. The Feulgen reaction hydrolyzes DNA to create these aldehyde sites, and Schiff’s reagent then binds to them, producing a magenta color wherever DNA is present. This makes the stain turn nuclei and chromosomal material distinctly, allowing visual confirmation of DNA in the tissue.

Other stains don’t target DNA specifically: Gram stain is for bacterial cell walls, PAS highlights carbohydrates, and silver stain is used for certain proteins, reticulin, or fungi depending on the protocol.