Answer: The correct answer for the fill in the blank is- Transcription.
Transcription is a genetic process by which DNA ( deoxyribonucleic acid) is converted into mRNA ( messenger RNA) with the help of enzyme RNA polymerase.
During this process, the two strands of DNA are first separated so that the template DNA ( that is having polarity 3' to 5') is exposed.
Using the template strand, RNA polymerase adds the RNA nucleotides according to the Watson and Crick base pairing and thus mRNA transcript is assembled.