Biology · Molecular Basis of Inheritance · NEET
NCERT lists exactly 4: (i) It should be able to make its own copy (Replication). (ii) It should be chemically and structurally STABLE. (iii) It should allow slow changes (Mutation) needed for evolution. (iv) It should be able to express itself in the form of Mendelian characters. A molecule must fulfil all 4 to act as genetic material.
Three reasons from NCERT. First, RNA has a 2'-OH group at every nucleotide; this -OH is a reactive group that makes RNA labile (easily broken). Second, RNA is catalytic (acts as ribozyme), so it is chemically reactive. Third, DNA has thymine in place of uracil, which gives DNA extra stability. So DNA is chemically less reactive and structurally more stable.
Yes, RNA can be a genetic material. In some viruses like Tobacco Mosaic Virus and QB bacteriophage, RNA is the genetic material. Both DNA and RNA satisfy all 4 criteria. But DNA is preferred for STORING genetic information because it is more stable, while RNA is better for TRANSMISSION (short-term expression).
DNA is double-stranded and the two strands are complementary. When heated, the strands separate. When the right conditions return, the complementary strands join back. This is why heat did not destroy the transforming principle in Griffith's experiment, showing DNA's stability.
RNA mutates at a faster rate because it is unstable. So RNA viruses with short life spans mutate and evolve faster. This is a NEET favourite: RNA = faster mutation, DNA = slower and more stable. Both can mutate, but RNA does it faster.
RNA can directly code for protein synthesis, so it can express characters easily. DNA cannot make protein directly; it depends on RNA. The whole protein-making machinery evolved around RNA. So for expression, RNA is direct; DNA works through RNA.
A molecule that can act as a genetic material must fulfill the traits given below, except
Try the real previous-year questions from this chapter — each with the answer and a full solution.
(i) Replication, (ii) Stability (chemical and structural), (iii) Mutation (scope for slow changes for evolution), (iv) Expression as Mendelian characters. Remember: Replicate, Stable, Mutate, Express.
DNA is better for storage because it is chemically and structurally more stable. RNA is better for transmission of genetic information because it is more reactive and can express characters directly.
Yes. NCERT states that the presence of thymine in place of uracil confers additional stability to DNA. This is one reason DNA is a better long-term genetic material than RNA.
Proteins fail at the very first criterion: they cannot make a copy of themselves (no replication). Only nucleic acids (DNA and RNA) can direct their own duplication using base pairing and complementarity.
RNA evolved first. There is strong evidence that essential life processes like metabolism, translation and splicing evolved around RNA. DNA was later derived from RNA. This is the RNA World Hypothesis, the next topic.
