Final answer:
A tagged version of a gene is created to monitor and understand the gene's expression within cells, which is critical for studying gene function, protein activity and for developing targeted therapies in personalized medicine.
Step-by-step explanation:
Taking DNA from just the expressed genes in a cell and making a cDNA library allows researchers to study which genes are active and the proteins they have the potential to encode. In a cDNA library, only the DNA that corresponds to mRNA (expressed genes) is included, which eliminates unexpressed regions, like introns and non-coding sequences, providing a focused view on important genetic information accountable for functional protein production.
One might want to make a tagged version of a gene to track its expression in cells, using reporter genes or tags that can be readily observed, such as GFP (green fluorescent protein), to explore the gene's function, location or the effects of its protein product in various contexts, including disease states like cancer. Tagging genes can help with the development of personalized medicine, where treatments are tailored based on individual gene expression patterns, and for understanding regulatory mechanisms like protein degradation signaled by ubiquitin tagging.
For example, in cancer cells, the expression of alternative forms of proteins can have serious consequences, leading to uncontrolled cell growth (as in the case of c-Flip protein variants in colon cancer). Applying this knowledge, targeted therapies have been designed to exploit the peculiarities of gene expression in cancer, such as medications antagonizing the EGF receptor in breast cancer.