Redrawing the Essentiality Map

Source: Hillenmeyer et al. (2008). The Chemical Genomic Portrait of Yeast: Uncovering a Phenotype for All Genes. Science 320: 362-365.

In the rich media generally used in the labs for growing yeast cells (e.g. YPD), in fact, ~80% of the yeast genome is dispensable with no evident phenotypic effect on growth. While this can be in part attributed to redundancy and robustness in the biological systems, we know that there aren't actually that many redundant pathways (let alone 80% of the genome). The most evident line of reasoning goes through the definition of "essentiality". Yeast cells, in their natural habitats, hardly ever encounter such a perfect environment such as a rich medium. Thus, the repertoire of seemingly non-essential genes, most probably, is essential in natural habitats and in different stress conditions.

In this paper, the authors have tested 1144 perturbtation conditions to identify the genes with phenotypic effects in homozygous and heterozygous contexts. It should be noted that although I'm not a fan of doing these experiments myself, I think they should be done (ofc0urse not by me). In their findings the authors report only 3% of genome with no growth effect in all these conditions. They show that most of these genes are generally inactive. Now, if you're interested in a certain gene, you should go to this database and do your study in a condition which bears a phenotype from this gene.

Apart from the concept of essentiality, they also look into the genes that are technically labeled as "Multi-Drug Resistance" genes. They define a set of 51 genes in this category which includes a set of known MDR genes.