Question

The concept of genes is not static but dynamic. Arrange the changing concept of genes chronologically - from earliest to the latest
(A) Gene is a sequence of nucleotides encoding functional products
(B) Isolation of nuclein by Friedrich Miescher
(C) One gene-one metabolic pathway block
(D) One gene-one polypeptide
Choose the correct answer from the options given below:

• A. (B), (A), (C), (D).
• B. (C), (B), (A), (D).
• C. (B), (A), (D), (C).
• D. (B), (C), (D), (A).

Hint:

Remember the historical timeline:
Miescher's Nuclein (1869) $\rightarrow$ Beadle & Tatum's One Gene-One Enzyme/Pathway (1941) $\rightarrow$ Ingram's One Gene-One Polypeptide (1957) $\rightarrow$ Modern Molecular Gene Concept.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Our scientific understanding of the gene has evolved continuously from a hypothetical unit of inheritance to a specific molecular sequence of nucleotides encoding functional RNA or protein molecules.

Step 2: Detailed Explanation:
Let us trace the chronological milestones of the gene concept:
- 1. (B) Isolation of nuclein by Friedrich Miescher (1869):
Friedrich Miescher isolated a phosphorus-rich substance from the nuclei of white blood cells, which he named "nuclein" (later identified as DNA). This was the earliest biochemical discovery related to genetic material.
- 2. (C) One gene-one metabolic pathway block (1941):
George Beadle and Edward Tatum proposed the "One gene-one enzyme" hypothesis based on their work with nutritional mutants of *Neurospora crassa*, showing that genes act by regulating specific chemical events in metabolic pathways.
- 3. (D) One gene-one polypeptide (1957):
Vernon Ingram demonstrated that sickle cell hemoglobin differed from normal hemoglobin by a single amino acid residue. This led to the refinement of the Beadle-Tatum hypothesis to the "One gene-one polypeptide" concept, recognizing that proteins can be multimeric.
- 4. (A) Gene is a sequence of nucleotides encoding functional products:
With the advent of modern molecular biology, sequencing, and the discovery of non-coding RNAs (tRNA, rRNA, lncRNA), the modern molecular definition arose, identifying the gene as a segment of DNA that is transcribed into a functional RNA or polypeptide.
Therefore, the chronological sequence is: (B) $\rightarrow$ (C) $\rightarrow$ (D) $\rightarrow$ (A).

Step 3: Final Answer:
The correct chronological sequence of the gene concept is (B), (C), (D), (A).