Biology · Biotechnology: Principles and Processes · NEET
Elution is the step where the separated DNA bands are cut out from the agarose gel and the pure DNA is extracted from those gel pieces. After gel electrophoresis sorts the DNA fragments by size, you still need to take the piece you want out of the gel, and elution does exactly that. Memory hook: "Electrophoresis SEPARATES, elution EXTRACTS" the fragment you want.
Elution is the last step: after electrophoresis separates the DNA bands, the wanted band is cut out from the gel and the pure DNA is extracted (eluted) for use in making recombinant DNA.
Your doubts, answered
Is elution the same as gel electrophoresis?
No. Gel electrophoresis is the technique that separates DNA fragments by size inside the gel. Elution is the next step: you cut out the band you want and take the pure DNA out of that gel piece. Electrophoresis separates, elution extracts.
What is the exact NCERT definition of elution?
NCERT says: the separated bands of DNA are cut out from the agarose gel and extracted from the gel piece, and this step is known as elution. So elution = cutting out the band + extracting the DNA from the gel.
Why is elution needed at all?
After electrophoresis the DNA is still trapped inside the solid gel. To use a fragment (the gene of interest) for making recombinant DNA, you must first get it out. The DNA fragments purified by elution are then joined with cloning vectors.
Does elution use ethidium bromide or UV?
No. Ethidium bromide staining and UV light are used before elution, only to see where the bands are. Elution itself is the cutting-out and extraction step. Do not confuse the visualisation step with the elution step.
Can eluted DNA be used to make recombinant DNA?
Yes. NCERT clearly states the DNA fragments purified by elution are used in constructing recombinant DNA by joining them with cloning vectors. NEET 2025 tested this exact idea and marked the statement correct.
⚠️ The NEET trap ✗ Elution means staining the DNA with ethidium bromide so the bands become visible under UV light. ✓ Staining with ethidium bromide and viewing under UV is the visualisation step. Elution is the separate step of cutting out the band and extracting the pure DNA from the gel piece. 🧠 NTA loves mixing the visualisation step (dye + UV) with the elution step (cut + extract). Remember: elution has nothing to do with the dye. It is scissors and extraction, done after you can already see the bands.
Real NEET questions
2022
Which one of the following statements is not true regarding gel electrophoresis technique?
A · The process of extraction of separated DNA strands from gel is called elution
B · The separated DNA fragments are stained by using ethidium bromide
C · The presence of chromogenic substrate gives blue coloured DNA bands on the gel ✓
D · Bright orange coloured bands of DNA can be observed in the gel when exposed to UV light
Solution: Statement (C) is not true. A chromogenic substrate giving blue colour belongs to the beta-galactosidase insertional-inactivation method of selecting recombinants, not to gel electrophoresis. Statement (A) is correct and is the definition of elution: extraction of separated DNA from the gel.
2025
Statement I: The DNA fragments extracted from gel electrophoresis can be used in construction of recombinant DNA. Statement II: Smaller size DNA fragments are observed near anode while larger fragments are found near the wells in an agarose gel. Choose the most appropriate answer.
A · Statement I is correct but statement II is incorrect
B · Statement I is incorrect but statement II is correct
C · Both statement I and statement II are correct ✓
D · Both statement I and statement II are incorrect
Solution: Both statements are correct. Statement I: DNA bands are cut out and eluted from the gel, and these purified fragments are used to make recombinant DNA with cloning vectors. Statement II: smaller fragments travel farther (towards the anode) while larger fragments stay near the wells.
Solved Biotechnology: Principles and Processes NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Elution is the step of cutting out the separated DNA bands from the agarose gel and extracting the pure DNA from those gel pieces.
What is the correct order of steps?
Cut DNA with restriction enzymes, then run gel electrophoresis to separate fragments by size, then stain with ethidium bromide and view under UV, then cut out and elute the wanted band.
Is elution part of downstream processing?
No. In NCERT, elution is a step in separation and isolation of DNA fragments during gene cloning. Downstream processing refers to separation and purification of the final expressed product before marketing.
What happens to the eluted DNA fragment next?
The purified eluted fragment (the gene of interest) is joined to a cloning vector using DNA ligase to form recombinant DNA.
Why can't you skip elution?
Because the DNA is trapped in the solid gel after electrophoresis. Without elution you cannot take the specific fragment out to use it in the next steps of recombinant DNA technology.
