Question

Large fragment of DNA (chromosome) is separated by

• A. Pulsed Field Gel Electrophoresis
• B. Agarose Gel Electrophoresis
• C. Polyacrylamide Gel Electrophoresis
• D. SDS- Polyacrylamide Gel Electrophoresis

Hint:

PFGE is a key tool in physical gene mapping, epidemiological typing of bacterial pathogens, and karyotyping of eukaryotic microbes.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Standard gel electrophoresis techniques separate molecules based on their rate of migration through a porous matrix under a constant electric field. However, very large DNA molecules (such as chromosomal fragments larger than 20–50 kb) migrate at the same rate in standard gels, preventing separation.

Step 2: Detailed Explanation:
- In standard agarose gel electrophoresis, large DNA molecules stretch out and migrate end-first through the gel pores at a uniform rate, regardless of size. This is called the "reptation limit."
- To separate megabase-sized DNA molecules (such as whole chromosomes), Pulsed Field Gel Electrophoresis (PFGE) is used.
- PFGE periodically changes the direction of the electric field.
- Every time the field changes direction, the large DNA molecules must reorient themselves to continue migrating through the gel pores.
- Larger DNA molecules take longer to realign than smaller ones, enabling effective separation of very large fragments (up to several megabases).

Step 3: Final Answer:
Large chromosomal DNA fragments are separated using Pulsed Field Gel Electrophoresis.