Given below are two statements
Statement I: Pre-1940, genes were considered to be like ‘beads-on-string’ and ‘not-divisible’.
Statement II: In 1940, CP Oliver proved that the genes are divisible.
In light of the above statements, choose the most appropriate answer from the options given below
Statement I: Pre-1940, genes were considered to be like ‘beads-on-string’ and ‘not-divisible’.
Statement II: In 1940, CP Oliver proved that the genes are divisible.
In light of the above statements, choose the most appropriate answer from the options given below
Show Hint
C.P. Oliver (lozenge gene) and Seymour Benzer (rII locus) are the two names most associated with proving gene divisibility.
- Both Statement I and Statement II are correct
- Both Statement I and Statement II are incorrect
- Statement I is correct but Statement II is incorrect
- Statement I is incorrect but Statement II is correct
The Correct Option is A
Solution and Explanation
The question asks about the historical perspective of gene structure and the transition from the classical gene concept to the modern concept of fine structure.
Step 2: Detailed Explanation:
• Classical Gene Concept (Statement I): Before 1940, based on the work of early geneticists like T.H. Morgan, genes were viewed as the ultimate, indivisible units of heredity.
They were thought to be arranged linearly on chromosomes like beads on a string.
It was believed that crossing over (recombination) could only occur between different genes, not within a single gene.
Mutations were also thought to involve the entire gene as a unit.
• Transition to the Modern Concept (Statement II): In 1940, C.P. Oliver conducted experiments with the lozenge (lz) locus in Drosophila melanogaster.
He observed rare wild-type progeny from crosses between two different mutant alleles of the same locus.
This demonstrated that recombination could occur within the boundaries of a single gene, meaning the gene is a divisible unit consisting of smaller sub-units (later defined as mutons and recons by Benzer).
This discovery paved the way for Seymour Benzer’s fine structure mapping of the rII locus in T4 bacteriophage.
Final Answer:
Statement I accurately describes the classical "beads-on-string" model pre-1940.
Statement II accurately describes the breakthrough work of C.P. Oliver in 1940 that disproved gene indivisibility.
Thus, both statements are correct.
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