Which factor would most directly cause no colonies on selective plates after transformation?

Which factor would most directly cause no colonies on selective plates after transformation?

• A. The plasmid lacks a functional antibiotic resistance gene
• B. The plates were incubated at optimal temperature
• C. The host cells were highly competent
• D. The antibiotic concentration matched guidelines

Answer: (A)

This question hinges on how selective plates function during transformation. To survive on plates that contain an antibiotic, the cells must carry a plasmid with a functional antibiotic resistance gene. If the plasmid lacks that functional resistance gene, the antibiotic will kill the cells regardless of plasmid uptake, so no colonies will form on the selective plates. The other factors influence how many colonies appear or whether growth occurs in general, but they don’t directly cause zero colonies when resistance is absent: optimal incubation temperature supports growth, high cell competency increases the chance of taking up a plasmid, and using the correct antibiotic concentration ensures proper selection—yet none of these will rescue cells that lack a functional resistance gene.

This question hinges on how selective plates function during transformation. To survive on plates that contain an antibiotic, the cells must carry a plasmid with a functional antibiotic resistance gene. If the plasmid lacks that functional resistance gene, the antibiotic will kill the cells regardless of plasmid uptake, so no colonies will form on the selective plates. The other factors influence how many colonies appear or whether growth occurs in general, but they don’t directly cause zero colonies when resistance is absent: optimal incubation temperature supports growth, high cell competency increases the chance of taking up a plasmid, and using the correct antibiotic concentration ensures proper selection—yet none of these will rescue cells that lack a functional resistance gene.