They arise in a unique subset of genes in which, after conception, the DNA in the embryo that came from the mother is expressed differently than the DNA from the father. (sciencemag.org)
To acquire and maintain its characteristic features, each cell type must express a unique subset of genes. (sciencedaily.com)
In order for these unspecialized cells to acquire the characteristics that make a leaf cell different from a root cell or a blood cell different from a muscle cell, they must turn on different subsets of genes to produce the proteins responsible for each cell type's distinctive properties. (sciencedaily.com)