A method of producing a polydeoxyribonucleotide molecule by reverse transcriptase polymerase chain reaction wherein the polydeoxyribonucleotide molecule has a length of greater than 5,000 base-pairs is disclosed. The method involves combining two reverse transcriptases followed by two protocols of polymerase chain reaction. This method enable the amplification of large DNAs, such as viruses, from a sample while preserving genetic diversity of the large DNA.