Question

Arrange the following terms/events chronologically based on their birth/discovery from the oldest to the latest.
• [(A).] 'DNA double helix' discovery 
• [(B).] Coining of the term 'Gene' 
• [(C).] Coining of the term 'Genetics' 
• [(D).] Reporting of the 'Pure line theory' 
Choose the correct answer from the options given below: 
 

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

Hint:

To remember Johannsen's contributions:
- He introduced the Pure line theory in 1903.
- He coined the terms Gene, Genotype, and Phenotype in 1909.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The history of genetics progressed through key discoveries that defined heredity, the physical units of inheritance, and the molecular structure of DNA.

Step 3: Detailed Explanation:
Let us review the historical dates for each event:
1. Reporting of the 'Pure line theory' (D): Wilhelm Johannsen proposed the pure line theory in 1903 through his selection experiments on the princess bean (Phaseolus vulgaris).
He showed that variation within a homozygous self-pollinated line is environmental rather than genetic.
2. Coining of the term 'Gene' (B): Wilhelm Johannsen coined the word "gene" (along with "genotype" and "phenotype") in 1909 to replace the term "factor" used by Mendel.
3. Coining of the term 'Genetics' (C): William Bateson coined the word "genetics" to describe the study of heredity and variation.
He first used the term in a letter in 1905, and it was officially introduced at the Third International Conference on Plant Hybridization in 1906.
4. Discovery of the 'DNA double helix' (A): James Watson and Francis Crick proposed the double-helix model of DNA in 1953, using X-ray diffraction data collected by Rosalind Franklin and Maurice Wilkins.
Let us analyze the options:
Since the discovery of the DNA double helix (1953) is definitely the most recent event, (A) must be last.
The pure line theory (1903) is the oldest event, so (D) must be first.
Among the options starting with (D) and ending with (A), Option (B) provides the sequence: (D) \(\rightarrow\) (B) \(\rightarrow\) (C) \(\rightarrow\) (A).

Step 4: Final Answer:
The correct chronological sequence is Option (B).