Define transformation efficiency in bacterial cloning. State the formula used to calculate it and illustrate with an example where 2 µg of plasmid DNA (size 3,000 bp) yields 1.2 × 10⁷ transformants on selective plates.

hard 3 marks Class 12 · Biology · Biotechnology Principles and Processes

Answer

Transformation efficiency = (Number of colonies

\times

Dilution factor) / (µg of DNA) = 6.0

\times

1 0^{6}

transformants per µg DNA

The correct answer is Transformation efficiency = (Number of colonies $\times$ Dilution factor) / (µg of DNA) = 6.0 $\times$ $1 0^{6}$ transformants per µg DNA — Thus the transformation efficiency is $6.0 \times 1 0^{6}$ transformants per µg of plasmid DNA.

Step-by-step solution

Transformation efficiency measures how many viable cells take up foreign DNA per microgram of DNA used.
Write the standard formula: $T E = \frac{Number of colonies \times Dilution factor}{µg DNA}$ .
In the example, the plates were counted directly, so the dilution factor is 1.
Plug the numbers: $T E = \frac{1.2 \times 1 0 ^{7} \times 1}{2 μ g}$ .
Perform the division: $\frac{1.2 \times 1 0 ^{7}}{2} = 6.0 \times 1 0^{6}$ .
Thus the transformation efficiency is $6.0 \times 1 0^{6}$ transformants per µg of plasmid DNA.

Common mistake: Omitting the dilution factor when colonies are counted from a diluted spread

Concept tested: Transformation efficiency definition

Published 1 October 2026 · How this solution was prepared and checked

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