Suggest how cells with the resistance gene might be selected.

• A. Expose cells to the fungus; non-resistant die, resistant survive
• B. Grow a random mixture and pick resistant colonies
• C. Identify by colony color change without any selection
• D. Expose cells to heat shock and select

Answer: (A)

Applying a selective pressure that only cells carrying the resistance gene can tolerate is the idea behind selecting for resistance. Exposing cells to the fungus creates that pressure: non-resistant cells die, while those with the resistance gene survive and can be isolated. This directly enriches for the trait because survival signals the presence of the gene. The other approaches lack a true selective step or rely on chance or screening rather than enrichment. Growing a random mixture and picking resistant-looking colonies isn’t reliable because there’s no guaranteed link between survival and the resistance gene, and you could miss true positives or pick false ones. A color change without any selection doesn’t enrich for the trait at all, and heat shock isn’t a specific test for the resistance gene unless it’s exactly the resistance being selected for, making it an unreliable method.