Yeast cells can be genetically engineered to produce human therapeutic proteins, such as insulin, using recombinant plasmids.

In a laboratory transfection experiment, researchers attempted to introduce a plasmid vector containing a selection marker gene and the human insulin gene into a culture of yeast cells. They determined the following:

• 1 in 160 yeast cells successfully took up a plasmid vector.
• Of the plasmids successfully taken up, only 1 in 625 actually contained the functional human insulin gene due to low ligation efficiency.