Yeast has been a very helpful organism for centuries, especially with respect to fermentation of sugars and production of bread. However, for an even longer time, yeast has been a distant relative of humans having diverged from a common ancestor, about one billion years ago. More than one third of the yeast genes have human counterparts, despite this evolutionary distance. Yeast and human orthologs perform the same or similar functions. Investigations have demonstrated that 9-92% of the amino acid sequences in similar human and yeast proteins overlap. However, even if two genes perform similar functions in two different organisms, it may not be possible to replace some of yeast genes with their human counterpart...