Which technique separates DNA fragments by size using electrical charges?

Which technique separates DNA fragments by size using electrical charges?

• A. Electrophoresis
• B. PCR
• C. Chromatography
• D. Spectroscopy

Answer: (A)

DNA fragments are separated by size with an electric field in a gel, a process known as electrophoresis. DNA’s phosphate backbone gives it a strong negative charge, so when an electric field is applied, the fragments move toward the positive electrode. The gel matrix acts like a sieve: smaller fragments navigate the pore spaces more easily and thus travel faster than larger ones, creating a size-based separation. This technique is routinely used with agarose gels for typical DNA fragment sizes, often alongside a DNA ladder to estimate relative sizes. Other options do different things—PCR amplifies selected DNA regions, chromatography relies on interactions with a stationary phase rather than an electric-field sieve, and spectroscopy analyzes how molecules interact with light rather than physically separating them by length.

DNA fragments are separated by size with an electric field in a gel, a process known as electrophoresis. DNA’s phosphate backbone gives it a strong negative charge, so when an electric field is applied, the fragments move toward the positive electrode. The gel matrix acts like a sieve: smaller fragments navigate the pore spaces more easily and thus travel faster than larger ones, creating a size-based separation. This technique is routinely used with agarose gels for typical DNA fragment sizes, often alongside a DNA ladder to estimate relative sizes. Other options do different things—PCR amplifies selected DNA regions, chromatography relies on interactions with a stationary phase rather than an electric-field sieve, and spectroscopy analyzes how molecules interact with light rather than physically separating them by length.