I was reading an article with title "using single cell sequencing data to model the evolutionary history of a tumor" bmcbioinformatics.biomedcentral.com/articles/10.1186/1471-2105-15-27. This article provide a computational method to infer the evolutionary mutation tree, incorporating the temporal order of mutation sites and single cell sequencing errors. Moreover, it estimates the proportion of time from the earliest mutation event of the sample to the most recent common ancestor (MRCA) of the sample of cells. It's here which confuses me. What is this MRCA of the sample of cells? Moreover, in the notes following table 1, "For example, 0,1 and 2 of the site for SESN2 represent DNA base composition of CC, CT, and TT, respectively". How to understand it then?