In the simplest terms, an exon is a segment of a gene that contains the information for making a protein. Your DNA is a long, continuous string of instructions, but it’s broken into pieces. Think of a gene as a string of Christmas lights: the exons are the bulbs that actually light up, while the introns are the plain wire in between.
When your cell wants to build a protein, it first copies the entire gene into a temporary message called pre-mRNA. This includes both exons and introns. Then, in a process called splicing, the cell snips out the introns and glues the exons together into the final, usable message—the mRNA that goes to the ribosome to make protein.
