Deoxyribonucleic acid (DNA) is composed of four types of nucleotide bases: adenine (A), cytosine (C), guanine (G) and thymine (T). The adenine (A) on one strand always pairs with the thymine (T) on the other strand, whereas cytosine (C) always pairs with guanine (G). The two strands are said to be complementary to one another. Accordingly, complimentary DNA (cDNA) is a copy of a strand of DNA containing a sequence of bases that bind to the original molecule. For example, if the original DNA stand had a base sequence of ATT, the complimentary DNA strand would carry a base sequence of TAA.

The production of complementary DNA is central to the replication of DNA, the making of two copies of the double stranded entity. In the process of DNA replication, the two strands are unzipped or unwound and...