Splicing
As noted, most of the genome is composed of introns interspersed with relatively few exons.
A critical step in the transcription process is called splicing, in which the introns are eliminated.
The remaining mRNA is translated into proteins, which are manufactured in the ribosomes.
From The National Center for Biotechnology Information (NCBI): A Science Primer http://www.ncbi.nlm.nih.gov/About/primer/est.html
