Exome: the part of the DNA that is transcribed into RNA and that remains after the RNA molecule undergoes liposuction. Well, not actual liposuction. DNA is like a book of blueprints, each blueprint being a gene; RNA represents a photocopy of a particular blueprint. The analogy, while useful, breaks down in the following way: the mature RNA molecule is not a perfect copy of its DNA template. It’s not that we go from colour to black-and-white but rather that whole pieces of the photocopy are removed.
Imagine a gene as a traffic cone: the orange segments are “exons” while the white segments are “introns”. When the gene, which is made of DNA, is transcribed into an RNA molecule (a photocopy of the original), the white segments or introns are removed and the nearest exons are joined together. This process is known as “splicing”. The mature RNA molecule is thus only made up of exons and is lacking the introns of the original gene. This RNA molecule will eventually be translated into a protein.
“Whole exome sequencing” is a fairly recent technique by which scientists can read the entire sequence (…AACTAGGCTAG…) of every exon in a person’s genome.