A.
Most protein-coding eukaryotic genes, in contrast, have their coding sequences interrupted by long, noncoding, intervening sequences called introns.
B.
The scattered pieces of coding sequence—called expressed sequences or exons—are usually shorter than the introns, and they often represent only a small fraction of the total length of the gene.
C.
Introns range in length from a single nucleotide to more than 10,000 nucleotides.
D.
Some protein-coding eukaryotic genes lack introns altogether, some have only a few, but most have many.