Consider the following statements and choose the correct statements using the codes given below :
"The genetic code is degenerate and universal" means:
A. Amino acids may have more than one codon.
B. All amino acids have more than one codon.
C. Codons are common for mostly all higher and lower organisms.

Question

Consider the following statements and choose the correct statements using the codes given below : 
"The genetic code is degenerate and universal" means: 
A. Amino acids may have more than one codon. 
B. All amino acids have more than one codon. 
C. Codons are common for mostly all higher and lower organisms.

Accepted Answer

The correct option is 2: A and C

The genetic code is a cornerstone of molecular biology, and understanding its key properties—degeneracy and universality—is essential. The phrase "The genetic code is degenerate and universal" is best described by statements A and C. Statement A correctly captures the meaning of degeneracy: **Amino acids may have more than one codon.** With 64 possible triplet codons but only 20 amino acids to code for (plus three stop codons), the mathematical necessity is that most amino acids are coded by multiple codons, often referred to as "synonymous codons." For instance, Leucine is coded by six different codons, illustrating this characteristic. This redundancy provides a critical buffer against potential point mutations, as a change in the DNA sequence may still result in the insertion of the correct amino acid. Statement C correctly defines universality: **Codons are common for mostly all higher and lower organisms.** The fact that the codon 'UAU' codes for Tyrosine in a bacterium, a plant, and a human is what makes the code universal. This highly conserved nature is what allows genetic engineers to take a gene from one species and express the functional protein in a completely different species, such as inserting the human insulin gene into bacteria.

The incorrect option is 1: B and C
This option is incorrect because statement B, **All amino acids have more than one codon**, is factually incorrect and contradicts the precise definition of degeneracy. While most of the 20 amino acids are coded by multiple codons, two specific amino acids, Methionine (coded only by AUG, which also serves as the start codon) and Tryptophan (coded only by UGG), are exceptions. They are encoded by only a single codon each. Therefore, because statement B is false, any option that includes it, such as B and C, must be an incorrect answer.

The incorrect option is 3: Only C
While statement C, **Codons are common for mostly all higher and lower organisms**, is a perfectly accurate description of the code's universality, the option "Only C" is incomplete for this question. The question specifically asks for the meaning of "degenerate *and* universal." A complete and correct answer must include an accurate description of both terms. Since statement A correctly describes degeneracy, choosing "Only C" ignores an equally important and correct component of the explanation.

The incorrect option is 4: Only A
Similarly, while statement A, **Amino acids may have more than one codon**, is an accurate and accepted definition of the code's degeneracy, the option "Only A" fails to address the second component of the phrase provided in the question. The question requires an explanation of why the code is "degenerate *and* universal." By only including statement A, this option provides no information regarding the universality of the genetic code (statement C), making it an incomplete and therefore incorrect choice for the full concept being tested.