Question

Given below are two statements:
Statement I : Functional alleles can complement to produce wild-type phenotype
Statement II : Heteroalleles are structurally and functionally non-allelic
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is correct but Statement II is false
• D. Statement I is incorrect but Statement II is true

Hint:

Functional complementation occurs between different cistrons; Heteroalleles represent different mutational sites within the same cistron (functionally allelic).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Seymour Benzer's $rII$ locus cis-trans complementation test in T4 bacteriophage defined the functional cistron and mutational sites.

Step 2: Detailed Explanation:
1. Statement I is correct: Two recessive mutations located in different functional units (different cistrons) complement each other in trans-heterozygotes to restore the normal wild-type functional phenotype.
2. Statement II is false: Heteroalleles (homoalleles vs heteroalleles) are mutations that occur at different nucleotide positions (structurally non-identical) within the same functional gene/cistron, meaning they are structurally non-allelic but functionally allelic (fail to complement).

Step 3: Final Answer:
Therefore, Statement I is correct but Statement II is false.