Recombinant DNA technology — vector capacity comparison Which of the following cloning vectors can maintain the largest fragment of foreign DNA for stable propagation during genetic engineering experiments?

Introduction / Context:
Different cloning vectors are engineered to carry foreign DNA inserts of varying sizes. Understanding vector capacity is essential when choosing the right tool for genomic library construction, physical mapping, and functional studies. This question asks you to identify which listed vector type accommodates the largest inserts while maintaining stability and selectable propagation in a suitable host.

Given Data / Assumptions:

• Common laboratory vectors include plasmids, bacteriophage λ derivatives, cosmids, BACs, and YACs.
• Insert capacity increases as you move from plasmids up to artificial chromosomes.
• Stability and ease of manipulation may trade off against maximum size.

Concept / Approach:

Typical insert ranges: plasmids (up to ~10 kb), λ phage vectors (~15–20 kb), cosmids (~35–45 kb), BACs (~100–300 kb), and YACs (often ~200 kb up to ~1–2 Mb). Although BACs are widely used for their stability and manageable handling, YACs have the highest theoretical capacity among the options, allowing cloning of extremely large genomic fragments that include centromeres, telomeres, and yeast autonomous replication sequences for maintenance in Saccharomyces cerevisiae.

Step-by-Step Solution:

Verification / Alternative check:

Historical genome mapping projects employed YAC libraries for megabase-scale inserts; later, BACs became popular for stability, but their capacity still falls below YACs’ upper range, confirming that YACs can maintain the largest fragments among these vector types.

Why Other Options Are Wrong:

Plasmids and phage vectors have limited capacity; cosmids carry more than plasmids but far less than artificial chromosomes. BACs are large-capacity but do not exceed YACs’ maximum insert capability.

Common Pitfalls:

Assuming BACs are the largest because they are commonly used today; “largest” refers to insert size, not popularity or stability.

Final Answer:

YAC (Yeast Artificial Chromosome)