One reason is because they reflect the activity levels of genes, which vary among different cell types despite containing the same genome. These differences in gene expression patterns are responsible for the diverse characteristics observed in cells and tissues, contributing to both normal physiology and disease states. Through comparing transcriptomes from various cell types or tissues, researchers can study how alterations in gene activity might influence disease progression. Additionally, transcriptome profiling can be used to evaluate the effects of drugs on gene expression patterns. By comparing transcriptomes before and after treatment, researchers can identify drug-responsive genes and predict drug efficacy.