Finding genes: cDNA

In many cases, especially in the early stages of exploring or comparing genomes, the focus is mainly on the genes rather than the whole genome sequence. So you might think it would be easier to study mRNA rather than DNA. However, mRNA and protein are both chemically unstable and therefore difficult to work with.

Instead, RNA is generally first converted into complementary DNA (cDNA). cDNA is a much more stable molecule, and because its sequence is identical to an mRNA's, it contains no introns. So cDNA represents only transcribed DNA sequence, i.e. the genes.