cDNA

You can make precise strands of a gene by making a complementary molecule of messenger RNA (mRNA). Remember that DNA contains sequences of code that are not of known value. The original mRNA made from the sense DNA stand had to be cleaned up, that is, the introns needed to be removed before a protein could be made. If you start off with the modified mRNA and use it to make a copy of the sense strand of DNA, you can produce an exact copy of the DNA gene. When DNA is made with this process, the DNA strand is known as complement DNA.