Synthetic defined media is commonly used in for the mainentence and proporgation of yeast. Drop out media is used for the selection of plasmids based on the use of auxotrophic mutant strains which cannot grow without a specific media component. Transformation with a plasmid containing the mutated gene enables the transformant to grow on a medium lacking the required component allowing for desired selections to occur.
Yeast can grow on a synthetic medium without any amino acids, however, better yield and growth rate can be achieved on richer media. In addition, a medium containing additional neutrients can increase the probability of successful transformations when screening libraries or performing gene knock-outs.
Synthetic defined drop out media is available both with and without agar for your convenience.