Insertion vectors (lambda): What is the maximum practical size of foreign DNA that can be cloned using a λ insertion vector?

Introduction / Context:
Lambda vectors come in two major formats for cloning: insertion vectors and replacement vectors. Insertion vectors retain most of the λ genome and accept relatively small inserts. Replacement vectors remove a stuffer fragment to accommodate much larger inserts. Knowing these capacities is crucial when selecting the right vector for a given fragment size.

Given Data / Assumptions:

• Packaging constraints require the total recombinant DNA to fit within the λ headful window.
• Insertion vectors accept small inserts; replacement vectors accept much larger inserts.
• Common insertion vectors (for example, λ gt10) typically handle inserts up to roughly the 7–10 kb range.

Concept / Approach:
Because insertion vectors keep most of the λ genome intact, only a limited additional size can be added while keeping the total within packaging limits. In practice, inserts much above ~10 kb are not suitable for insertion vectors and should be moved to replacement formats.

Step-by-Step Solution:

Verification / Alternative check:
Cloning guides for λ insertion vectors recommend inserts in the vicinity of several kilobases, and commonly state inefficiency beyond ~10 kb, whereas replacement vectors target ~15–20+ kb up to ~40 kb.

Why Other Options Are Wrong:

Common Pitfalls:
Attempting large genomic fragments in insertion vectors and obtaining very low packaging or plaque yields.

Final Answer:
About 10 kb.