It is in the sequence of the nucleotides in the polymers where the genetic information carried by chromosomes is located. One DNA strand can be up to several hundred million nucleotides in length. An important point of emphasis should be that all vegetative cells of one organism contain the same genetic information. However, the specific genes that are expressed at specific times may be very different between different tissues. These differences in gene expression allow for the regulation of development of the organism, and for the development of different tissues.
Transcription starts at a specific site on the DNA called a promoter.
The introns may be anywhere between 50 and 10,000 nucleotides in length. The coding regions of the mRNA are called exons. There may be up to 100 introns in a single gene. However, in prokaryotes introns are rare and mRNA generally does not get processed before translation. In addition to rRNA, there are some 70 different proteins in a ribosome.