Genetic engineering fundamentals: In cloning and gene delivery, what best defines a “vector” used to carry foreign DNA into host cells?

Introduction / Context:
A vector is the workhorse of recombinant DNA technology. Whether plasmid, bacteriophage, cosmid, BAC, YAC, or viral delivery system, the vector must accept a foreign DNA insert and introduce it into a host where replication or expression can occur. Understanding what a vector is (and is not) is foundational for molecular biology labs and biotechnology applications.

Given Data / Assumptions:

• Vectors possess defining features such as an origin of replication, selectable markers, and one or more cloning sites.
• They are engineered to stably maintain and propagate inserted DNA.
• Delivery can be by transformation, transfection, electroporation, or infection.

Concept / Approach:
Correctly define a vector as a DNA molecule designed to carry foreign DNA. The vector must be able to form stable, covalently closed constructs with the insert (via ligation or recombination) and to deliver and maintain that DNA inside competent host cells under selection. Many vectors also include promoters for expression, tags for purification, and recombination sites for efficient subcloning.

Step-by-Step Solution:

Verification / Alternative check:
Restriction mapping, PCR screening, and sequencing of recovered plasmids confirm that the vector has successfully carried and maintained the foreign insert within host populations.

Why Other Options Are Wrong:

• Degrading nucleic acids: describes nucleases, not vectors.
• “Help in replication” is incomplete; many molecules assist replication, but a vector is specifically a DNA carrier for foreign inserts.
• Protecting host cells from foreign DNA: the opposite of vector function.
• Small RNAs: can regulate genes but are not general cloning vectors.

Common Pitfalls:
Confusing antibiotic resistance as the only vector property; it is merely a selectable marker. A true vector must enable stable propagation or expression of the inserted DNA.

Final Answer:
Molecules that can covalently carry foreign DNA and deliver it into cells