Which of the following is not listed as a cause of a smear on an agarose gel?

Which of the following is not listed as a cause of a smear on an agarose gel?

• A. Degraded DNA.
• B. Overloading the gel with too much sample.
• C. Non-specific amplification.
• D. High-purity DNA.

Answer: (D)

Seeing a smear on an agarose gel means the DNA sample contains fragments of many different sizes rather than one uniform size. Intact, high-purity DNA usually produces a clean, discrete band at a specific size. Degraded DNA breaks into multiple pieces, creating a range of fragment lengths that smear across the gel. Overloading the gel with too much sample can cause diffusion and matrix saturation, also giving a smeared appearance. Non-specific amplification generates a mix of unintended products of various lengths, which shows up as a smear as well. High-purity DNA, lacking these issues, does not cause a smear; it tends to give a sharp band.

Seeing a smear on an agarose gel means the DNA sample contains fragments of many different sizes rather than one uniform size. Intact, high-purity DNA usually produces a clean, discrete band at a specific size. Degraded DNA breaks into multiple pieces, creating a range of fragment lengths that smear across the gel. Overloading the gel with too much sample can cause diffusion and matrix saturation, also giving a smeared appearance. Non-specific amplification generates a mix of unintended products of various lengths, which shows up as a smear as well. High-purity DNA, lacking these issues, does not cause a smear; it tends to give a sharp band.