Question

question 3
how does a dna stain make dna fragments visible in gel electrophoresis?
a the stain reacts chemically with the dna, changing its color
b the stain attaches to dna and fluoresces (emits light) when exposed to a specific light source
c the stain alters the electrical charge of dna, making it move faster
d the stain increases the size of the dna fragments, making them easier to see

Explanation:

DNA stains like ethidium bromide attach to DNA. When exposed to ultraviolet (a specific light source), they fluoresce (emit light), allowing DNA fragments to be visible. Option A is incorrect as it's not a simple chemical color - change reaction. Option C is wrong because stains don't alter DNA's electrical charge for faster movement (charge is due to phosphate groups in DNA backbone). Option D is incorrect as stains don't increase DNA fragment size.

Answer:

B. The stain attaches to DNA and fluoresces (emits light) when exposed to a specific light source