Question

During the course of evolution why DNA was chosen over RNA as genetic material? Give reasons by first discussing the desired criteria in a molecule that can act as genetic material and in the light of biochemical differences between DNA and RNA.

Answer 1

$\text{Criteria for a molecule to be a genetic material}$

The following criteria need to be fulfilled for any molecule to be a genetic material:

• It should be able to generate its copy, that is, it should replicate itself.
• It should be chemically and structurally stable.
• It should show a scope of slow changes such as mutations because this helps in generating variations which are important for evolution.
• It should be able to express itself in the forms of Mendelelian characters.

$\text{Reasons for DNA as a better genetic material:}$

• DNA contains 2'H in deoxyribose sugar which makes it chemically stable as compared to RNA that contains 2'-OH in ribose sugar which is chemically reactive.
• Thymine in DNA is less susceptible to tautomerism and mutations as compared to uracil in RNA.
• RNA shows catalytic properties that are absent in DNA.