The characteristics features of genetic code are i. It is always universal ii. It is triplet of nucleotides bases corresponding to 20 amino acids iii. It is non-overlapping, non-ambiguous and commaless iv. It has start and stop codon Which of the statements given above are true?
- (a)i, ii and iv only
- (b)i, iii and iv only
- (c)i, ii and iii only
- (d)All of the above
Correct — D, all four statements are true, so the answer is 'All of the above'. (i) The code is (near-)universal — the same codons specify the same amino acids in almost every organism, from bacteria to humans. (ii) It is a triplet code — each amino acid is read as a group of three nucleotide bases (a codon); the 64 possible codons together specify the 20 standard amino acids. (iii) It is non-overlapping (each base is read only once), non-ambiguous/unambiguous (one codon codes for only one amino acid) and commaless (read continuously with no gaps). (iv) It has one start codon (AUG) and three stop codons (UAA, UAG, UGA). For NCERT/exam purposes universality is treated as a defining feature, so the commission's key counts every statement as correct.
- (a)i, ii and iv only — Leaves out statement (iii) — the code IS non-overlapping, unambiguous and commaless — so this option is incomplete.
- (b)i, iii and iv only — Omits statement (ii), the triplet-code fact (3 bases per codon for 20 amino acids), which is true — so it is incomplete.
- (c)i, ii and iii only — Omits statement (iv) — the code does have a start codon (AUG) and stop codons (UAA/UAG/UGA) — so it is incomplete.
The genetic code is the set of rules by which the four-letter nucleotide sequence of mRNA is translated into the 20-amino-acid language of proteins. Bases are read three at a time (codons); with 4 bases there are 4x4x4 = 64 codons for 20 amino acids, so most amino acids have more than one codon — this redundancy is called degeneracy.
The question lists the classic 'salient features' of the code straight from NCERT Biology, and every one is a standard textbook feature — so the safe read is that all statements are correct. The trap is to reject statement (i) because the code is only 'nearly' universal (rare exceptions exist, e.g. in mitochondria); but at the NCERT/MPPSC level the code is taught as universal.
- Triplet code: 3 bases = 1 codon; 64 codons specify the 20 standard amino acids.
- Start codon = AUG (also codes methionine); stop codons = UAA, UAG, UGA.
- Properties: universal, non-overlapping, unambiguous, commaless and degenerate.
- Decoded in the 1960s; the 1968 Nobel Prize in Medicine went to Nirenberg, Khorana and Holley.
All four features hold — hence the answer is 'All of the above' (D).
- Calling the code 'overlapping' — it is non-overlapping
- Forgetting AUG doubles as the start codon and codes methionine
- Assuming one amino acid = one codon (this ignores degeneracy)
MPPSC/UPSC ask 'which features of the genetic code are correct' or 'match the codon (AUG/UAA) to its role' — lock the four properties plus the start/stop codons.
No directly related past PYQ was found.
- practice — not a real PYQ
In the standard genetic code, how many codons are 'sense' (amino-acid coding) and how many are stop codons?
- (a)61 coding + 3 stop
- (b)64 coding + 0 stop
- (c)20 coding + 44 stop
- (d)60 coding + 4 stop
Answer(a) 61 coding + 3 stop — 64 codons in all, minus the three stop codons.
- practice — not a real PYQ
The property by which more than one codon can code for the same amino acid is called:
- (a)Degeneracy (redundancy)
- (b)Ambiguity
- (c)Overlapping
- (d)Universality
Answer(a) Degeneracy — several codons can specify one amino acid.