Transformation is the process by which exogenous DNA is introduced into a cell, resulting in a heritable change or genetic modification. This was first reported in Streptococcus pneumoniae by Griffith in 1928. Transforming principle of DNA was demonstrated by Avery et al. in 1944.
The development of genetic engineering and cloning has opened many possibilities of expression and isolation of heterologous proteins for research purposes. Considerable advances in technology have enabled expression and isolation of recombinant proteins in large scale.
The selection of plasmids in yeast is based on the use of auxotrophic mutant strains, which cannot grow without a specific medium component (an amino acid, purine, or pyrimidine)
Yeasts are considered model systems for eukaryotic studies as they exhibit fast growth and have dispersed cells.