What is the difference between introns and exons?

Exons are the coding sequences of a gene that are retained in mature mRNA and translated into protein, while introns are intervening non-coding sequences that are removed during RNA splicing. Eukaryotic genes typically contain multiple introns and exons, with introns often much longer than exons. Alternative splicing allows different combinations of exons to produce multiple protein isoforms from a single gene. Prokaryotes generally lack introns, though some are found in archaeal and bacterial genes.