Final answer:
RNA sequencing (RNA seq) is the best method for determining which genes are being transcribed in a particular cell type.
Step-by-step explanation:
The best method for determining which genes are being transcribed in a particular cell type is RNA sequencing (RNA seq). RNA sequencing allows scientists to study the entire collection of mRNA molecules produced by cells, providing information on the genes that are actively transcribed in a specific cell type. By sequencing the RNA molecules, researchers can identify and compare the gene expression patterns between different cell types.