What is not true for genetic code?

Options

A. It is degenerate.
B. It is nearly universal.
C. A code in mRNA is read in a noncontiguous fashion.
D. It is unambiguous.

Answer

To determine what is not true for genetic code, let's analyze each of the given options step by step.

### Step-by-Step Solution:

1. **Understanding Genetic Code**:
- The genetic code consists of codons, which are sequences of three nucleotides in mRNA that correspond to specific amino acids. There are a total of 64 possible codons (4^3 combinations), but only 61 of these codons specify amino acids, while 3 are stop codons.

**Hint**: Remember that codons are triplets of nucleotides that code for amino acids.

2. **Evaluating the Options**:
- **Option 1: It is degenerate**:
- This statement is true. The genetic code is degenerate because multiple codons can code for the same amino acid. For example, there are four codons that can code for proline.

**Hint**: Degeneracy means that multiple codons can specify the same amino acid.

- **Option 2: It is nearly universal**:
- This statement is also true. The genetic code is nearly universal, meaning that most organisms use the same codons to code for the same amino acids, although there are some exceptions in certain organisms.

**Hint**: Universality indicates that the same codons are used across different species.

- **Option 3: A code in mRNA is read in non-contiguous fashion**:
- This statement is false. The genetic code is read in a contiguous fashion, meaning that the ribosome reads the mRNA in a sequential manner without skipping any nucleotides.

**Hint**: Contiguous reading means that the sequence is read one after another without interruption.

- **Option 4: It is unambiguous**:
- This statement is true. The genetic code is unambiguous because each codon specifies only one amino acid. For example, the codon AUG always codes for methionine.

**Hint**: Unambiguity means that each codon has a specific and unique meaning.

3. **Conclusion**:
- Based on the evaluation, the statement that is not true for the genetic code is **"A code in mRNA is read in non-contiguous fashion."** Therefore, this is the correct answer.

### Final Answer:
The statement that is not true for genetic code is: **A code in mRNA is read in non-contiguous fashion.**