A series of experiments conducted proved that both RNA and DNA serve as genetic material. For a molecule to be a genetic material, it should be structurally and chemically stable, it should provide scope for slow changes or mutation, it should be able to express itself in Mendelian characters and also be able to generate its own replica.
Most biomolecules including proteins fail to fulfil the criteria, but the DNA and RNA meet all these requirements. Even though DNA serves predominantly as the genetic material, RNA also acts as the genetic material in a few microbes and also performs the role of a messenger and adapter.
It is the DNA that transformed the R-strain bacteria to living S-strain in Griffith’s experiment. Though the transformation killed the mice, it had not changed the properties of the DNA. This makes evident of the stable structure of DNA. Although it is separated by heat exposure, it can come together under suitable conditions. DNA has thymine instead of uracil present in RNA, which makes it more stable. So, it is said that DNA has evolved from RNA with chemical modifications, making it more stable and as a result, a better genetic material.
On the other hand, RNA is much more liable to change due to the presence of the very reactive 2’-OH group that is present in all its nucleotides. This makes RNA more degradable and reactive than DNA. Yet, both DNA and RNA can mutate. However, viruses with RNA genome evolve faster by mutation due to the ability of RNA to mutate quickly on account of its relative instability. But, DNA is dependent on RNA to synthesise the proteins through transcription and translation. Even other life processes such as metabolism, translation and splicing are evolved around RNA. Therefore, even though DNA is the preferred genetic material due to its stability, it is the RNA that is involved in the transmission of genetic information.