**Core Concept**
The question is based on the **genetic code**, which is the set of rules used by living cells to translate information encoded within **genetic material** (DNA or RNA sequences) into **proteins**. **Nucleotide sequences** are translated into **amino acid sequences**. The genetic code is nearly universal and determines how **sequences of nucleotides** correspond to **amino acids**.

**Why the Correct Answer is Right**
If a constitutive sequence of 4 nucleotide codes for 1 amino acid, this implies a **quadruplet code**. With 4 nucleotides (A, T, G, C) and a sequence of 4, the number of possible combinations is 4^4 = 256. However, since the question asks about amino acids and assuming a direct, non-degenerate coding (which is not how the standard genetic code works but following the hypothetical scenario), the calculation directly gives the number of unique sequences possible.

**Why Each Wrong Option is Incorrect**
**Option A:** This option does not match the calculation for the number of combinations possible with a quadruplet code.
**Option B:** Similarly, this does not align with the calculated possibilities from a 4-nucleotide sequence.
**Option C:** This option is also incorrect as it does not reflect the outcome of the calculation based on the given scenario.

**Clinical Pearl / High-Yield Fact**
In the actual **genetic code**, a sequence of 3 nucleotides (triplet) codes for 1 amino acid, and this code is degenerate, meaning more than one triplet can code for the same amino acid. Understanding the basics of the genetic code is crucial for appreciating how genetic information is translated into proteins.

**Correct Answer:** Correct Answer: D. 256