The exome is a subset of the genome that contains many of the most important DNA sequences: the portions of genes that encode proteins. Most genes do not encode proteins using a single continuous stretch of DNA. Typically, a gene will encode a protein using multiple distinct stretches of DNA; the information in these separated stretches of DNA is then pieced together to direct production of a protein.
The stretches of the gene that are used to direct protein production are called “exons”. Exons are also referred to as the coding region of a gene because they encode the information for a protein. The stretches of genes that do not encode proteins are called “introns” and are one kind of noncoding DNA sequence. The exons of all our genes make up approximately 1.5% of our genome and are collectively referred to as the “exome”.
Because the exome is a small percentage of the entire genome, it is cheaper and faster to sequence the exome then the entire genome. While the exome contains many of the most important DNA sequences for understanding biological processes, there are some important DNA sequences that are not contained within the exome. There are regions of noncoding DNA that have important biological functions, such as regulating the coding regions of the genome. Ongoing research is investigating the functions of different regions of noncoding DNA.