This selective activation allows cells to adopt specific functions in the body, determining whether they become—for example—heart cells, muscle cells, or brain cells. However, these enhancers don't always turn on the right genes at the right time, contributing to the development of genetic diseases like cancer and diabetes. Beer's team was specifically interested in understanding how enhancers influence "cell fate decisions," or the process when one cell transitions into another cell type during development. Errors in cell fate decisions are a major factor in disease development. Next, they used the CRISPR gene-editing system to disrupt or stimulate potential enhancers and observe the effects on gene expression.