Vector stability in yeast — which is most genetically stable in vivo? Among common Saccharomyces cerevisiae vector systems, which type is generally the most stable because it integrates into the host genome?

Introduction / Context:
Different yeast vector classes balance copy number, stability, and ease of selection. Stability refers to faithful maintenance of genetic information over many cell divisions without selection pressure.

Given Data / Assumptions:

• YIp vectors integrate into the yeast genome via homologous recombination.
• YEp vectors replicate episomally using 2μm sequences and can be lost without selection.
• YRp vectors with ARS can be unstable due to poor segregation.
• YCp vectors behave like mini-chromosomes but can be lost at low frequency.

Concept / Approach:

Integration into the host genome provides maximal genetic stability because the inserted sequence segregates with chromosomes. Episomal or ARS-based plasmids can be diluted or mis-segregated over time, particularly without selective pressure. Therefore, YIp is typically the most stable choice for long-term maintenance.

Step-by-Step Solution:

Verification / Alternative check:

Yeast genetics manuals recommend YIp for gene replacement or stable integration, reflecting empirical stability compared with plasmid-based systems.

Why Other Options Are Wrong:

YEp/YRp may be lost without selection; YCp is fairly stable but still episomal; YACs are large and can undergo rearrangements.

Common Pitfalls:

Equating high copy number with stability; higher copy often increases instability, not the reverse.

Final Answer:

YIp (yeast integrative plasmid)