The differences in our cells don\u2019t come from differences in the genes themselves: Every cell in your body contains a copy of your distinctive DNA and the 20,000 genes for making proteins it encodes. \u201cThe genome is a parts list,\u201d Quake said. \u201cThere\u2019s no way to predict which cell types come out of a given genome.\u201d<\/p>\n

To distinguish a white blood cell from a muscle cell at the molecular level, scientists have to look at the cell\u2019s RNA. RNA transcripts that are copied from DNA sequences ferry the instructions for building proteins to the ribosome, the cell\u2019s protein construction center. Therefore, RNA transcripts contain the information about which genes are active and expressed in a particular cell.<\/p>\n

Using a powerful set of single-cell genomics tools, scientists can read these expression patterns to fingerprint a cell. These tools have matured over the past few years so that scientists can now quickly and efficiently look at tens of thousands or even millions of cells in a single experiment.<\/p>\n

\u201cOnce that was in place, then there\u2019s nothing stopping you from making an atlas,\u201d Quake said. \u201cIt all just kind of cascaded.\u201d<\/p>\n