In the coding dictionary, there are 64 codons as `:`

Options

A. 64 amino acids are to be coded
B. 64 types of tRNAs are present
C. there are 44 non - sense codons and 20 sense codons
D. genetic code is triplet

Explanation

To solve the question regarding the coding dictionary and the nature of codons, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Codons**:
- Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids or stop signals during protein synthesis.

2. **Initial Hypothesis**:
- The question mentions a scenario where codons are considered to be doublets (two nucleotides). If we assume that codons are made of two nucleotides, we can calculate the number of possible combinations.

3. **Calculating Doublet Codons**:
- Each nucleotide can be one of four types (A, U, C, G). Therefore, for doublet codons, the total combinations would be calculated as:
\[ 4^2 = 16 \text{ combinations} \]
- This means that if codons were doublets, we could only code for a maximum of 16 different amino acids.

4. **Identifying the Limitation**:
- Since there are more than 20 amino acids in nature, the doublet codon system would not suffice to code for all amino acids.

5. **Transition to Triplet Codons**:
- To resolve the limitation of the doublet system, we consider the triplet codon system. This means each codon consists of three nucleotides.

6. **Calculating Triplet Codons**:
- For triplet codons, the total combinations would be:
\[ 4^3 = 64 \text{ combinations} \]
- This allows for coding of up to 64 different amino acids, which is more than sufficient to cover the 20 standard amino acids and additional stop signals.

7. **Conclusion**:
- The genetic code is therefore established as triplet in nature, which explains the existence of more than 20 amino acids.

### Final Answer:
The genetic code is triplet in nature.

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