The expression of a gene is said to be 'turned on' when certain signals interact with the promoter of a gene and RNA is produced. The strand of RNA that corresponds to a gene is complementary to the sequence of DNA. The process called "Transcription" is:

Transcription is the process of forming an RNA molecule from a DNA template molecule. In this process, the DNA strands separate and one serves as a template for the RNA, while the other is inactive. At the end of the transcription, the tapes that were separated are joined again.