Definition of the “stuffer” fragment in λ replacement vectors In lambda replacement cloning systems, the term “stuffer” refers to which part of the vector DNA?

Introduction / Context:
Replacement vectors in the λ system swap out a dispensable central region—called the stuffer—for foreign DNA. Recognizing this component is key to understanding how these vectors accommodate larger inserts than insertion vectors.

Given Data / Assumptions:

• λ genome is divided into left and right arms that flank a central stuffer piece.
• Packaging requires the final recombinant DNA to fall within length limits.
• The stuffer is designed to be replaced during cloning.

Concept / Approach:
Because the stuffer is nonessential for phage propagation in the recombinant context, it can be removed to create space for an insert. The two arms plus the insert must satisfy packaging constraints for viable phage production.

Step-by-Step Solution:

Verification / Alternative check:
Maps of replacement vectors clearly label a central “stuffer” region that is excised during library construction.

Why Other Options Are Wrong:

• Left/right arms are retained; they are not the stuffer.
• MCS or resistance cassettes are separate features.

Common Pitfalls:
Confusing insertion vectors (which do not remove a stuffer) with replacement vectors.

Final Answer:
The central fragment that is removed and replaced by the foreign insert