Transcription is the process of formation of RNA from the DNA. In this process, only one strand of DNA is used called as template strand which has polarity 3' to 5'. The segment of DNA that takes part in transcription is called as transcription unit in which have promoters at the 5' end of coding or 3' end of template strand, structural gene and then terminator sequence. The promoter provides the binding site to the RNA polymerase enzyme for transcription. The single base DNA difference in the human genome is called as single nucleotide polymorphism.