Transformation, Selection, and Clone Screening
DNA Uptake into Cells
Transformation methods
DNA can be introduced by chemical transformation, electroporation, transfection, microinjection, lipofection, or viral delivery depending on the host system. Method choice affects throughput, cell viability, and fragment size tolerance.
Selection and screening strategies
| Strategy | Purpose | Typical readout |
|---|---|---|
| Antibiotic selection | Enrich for cells carrying vector | Growth on selective medium |
| Blue-white screening | Distinguish insert-containing clones | Color change from reporter disruption |
| Colony PCR | Rapid insert check | Amplicon size |
| Restriction digest | Confirm insert pattern | Fragment sizes after digestion |
| Sequencing | Verify exact construct | Base-level validation |
Selection is not validation
A resistant colony or positive screen can still contain rearrangements, point mutations, or mixed plasmid populations. Final sequence confirmation is essential.
Which method provides the highest-confidence confirmation of a cloned construct?
Sequence-based validation directly tests the construct at nucleotide resolution.
Correct answer: Sanger or next-generation sequencing
Why might electroporation be chosen over chemical transformation?
Electroporation transiently permeabilizes membranes and often improves uptake.
Correct answer: It can provide higher efficiency for difficult hosts or larger DNA molecules.
Blue-white screening is typically based on disruption of which kind of function?
Insertional disruption of a reporter enables visual screening.
Correct answer: A reporter gene activity in the cloning site
Name one reason colony PCR can be misleading.
PCR only samples part of the construct.
Correct answer: It may amplify contaminating template or fail to detect rearrangements outside the amplified region.