The information contained in DNA is used to synthesize proteins that are necessary for the functioning of life. DNA is composed of four nucleotides: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). The information contained in DNA can then be thought of as a sequence of these four nucleotides. DNA has coding and non-coding regions. Coding regions — where the sequence of these nucleotides are read in groups of three to produce individual amino acids — constitute only about 2% of human DNA. For example, the triplet of nucleotides CCG codes for the amino acid glycine, while the triplet GGA codes for the amino acid proline. Three nucleotides are then assembled to form a protein.
Based only on the information provided above, which one of the following statements can be logically inferred with certainty?
A. Only (i): The majority of human DNA has a function about which we currently have no understanding.
B. Only (ii): The function of human DNA is not fully understood.
C. Both (i) and (ii).
D. Only (iii): The triplet of nucleotides CCG codes for the amino acid glycine.
GATE 2023 · General Aptitude · Logical Reasoning · medium
Answer: D. Only (iii): The triplet of nucleotides CCG codes for the amino acid glycine.
Identify explicitly stated facts: From the passage: (a) DNA has 4 nucleotides A, T, C, G. (b) Coding regions = 2% of human DNA. (c) Triplets in coding regions code for amino acids. (d) CCG codes for glycine. (e) GGA codes for proline.
Evaluate statement (i): majority of DNA has unknown function: The passage says non-coding = 98%. It does NOT say non-coding regions have no known function or unknown function. Non-coding DNA can have regulatory, structural, or other roles not mentioned. Statement (i) cannot be inferred — NOT certain.
Evaluate statement (ii): function of DNA not fully understood: The passage makes no claim about our level of understanding of DNA. It only describes the coding mechanism. Statement (ii) imports scientific knowledge not in the passage — NOT certain.
Evaluate statement (iii): CCG codes for glycine: The passage explicitly states: 'the triplet of nucleotides CCG codes for the amino acid glycine.' This is a direct, verbatim fact from the passage. CERTAIN.