Final answer:
The presence of a selectable marker on the plasmid allows the researcher to determine if the transformed cells have taken up the plasmid. By plating the cells on a solid medium containing the antibiotic, the researcher can distinguish between cells that have the plasmid and cells that do not.
Step-by-step explanation:
The presence of a selectable marker on the plasmid allows the researcher to determine if the transformed cells have taken up the plasmid. Selectable markers, such as antibiotic resistance genes, are included on the plasmid along with the gene of interest. This means that only cells that have successfully taken up the plasmid will be able to grow in the presence of the antibiotic. By plating the cells on a solid medium containing the antibiotic, the researcher can distinguish between cells that have the plasmid and cells that do not.
For example, if the plasmid contains an ampicillin resistance gene, only cells that have taken up the plasmid will be able to grow on a medium containing ampicillin. This allows the researcher to select and identify the transformed cells for further analysis.