This process, called genetic transformation , played a critical role in the history of molecular biology and the discovery that DNA was the genetic material. Today, transformation is not limited to bacteria, and in fact, is used routinely by molecular biologists to manipulate and study the behavior of genes. As a model system, yeast has the advantage over bacteria, of being a eukaryotic organism with subcellular organization like that of plants and animals, including humans.
Yeast transformation involves several steps.
This experiment uses a yeast strain which is defective in an adenine synthesis gene, ADE1 . The metabolic defect in the mutants causes them to require adenine for growth and to accumulate a red pigment which causes the colonies to appear pink or red in color. When these ade1 mutant yeast are transformed with the normal ADE1 gene, they gain the ability to grow in the absence of adenine and form normal cream colored colonies. They behave in many ways like real chromosomes which carry genes in cells but plasmids are much more convenient. The YCpADE1 plasmid exists in one copy in a haploid yeast cell, just like the normal chromosomes, and since it carries a yeast centromere, will be stably sorted into the daughter cells each time the yeast divides.