Exons are sequences on the primary transcript, or pre-mRNA (or the DNA sequence from which it is transcribed), that remain in the RNA after RNA processing. Introns are sequences on the primary...
The exon - the 'coding' DNA sequence - is 'determined' by the Dna that is Expressed. The introns - noncoding DNA sequences - are returned for recycling.
Exons are part of both prokaryotic and eukaryotic. Introns are rarely present in the domain bacteria (common bacteria) while introns are present in some genes in domain archaea ("ancient" bacteria)....
Exons are the DNA sequences that code for proteins. Introns are involved however they dont carry the genetic information that exons carry, the variation provides for revolutionary flexibility...