As noted above, transformation is an inefficient process, so researchers want to make
the most of every cell that has been transformed. In our experiments, we will be isolating transformed cells for their ability to grow in the absence of uracil, but we are really interested
in their ability to grow in the absence of Met. Replica plating offers a means to quickly screen a plate of cells for their ability to grow in a wide range of media, while retaining information about individual colonies. As shown on the opposite page, the original plate of transformants becomes the “master plate.” An imprint of the master plate is made by GENTLY tapping the inverted
plate on a piece of sterile cotton velveteen immobilized on a block. This imprint can then be transferred to plates with different kinds of selective media, establishing the genotype of the transformants. In our experiments, we will make transfer replicas of the transformation reactions (isolated on YC-Ura plates) to YC-Ura plates that are also lacking Met, with either glucose or galactose as a carbon source.
Replica plating provides a rapid screening method for analyzing phenotypes.
Colonies on a master plate are transferred to a sterile piece of velveteen. Copies of the mater plate are transferred
to additional selective or indicator media to monitor phenotypes under additional conditions.