The human body contains more than 30 trillion cells. Until recently, the sheer number of cells in the organism meant that approaches to understanding human diseases and developmental processes based on the analysis of single cells were a futuristic vision. The development of new sequencing methods is currently revolutionising our understanding of cellular heterogeneity. These technologies can detect rare or even new cell types by extracting and sequencing the genetic information from the cells based on ribonucleic acid chains.