Select the option that correctly represents: coding sequence of DNA and Non- coding sequence of DNA, respectively.

Options

A. exon, intron
B. intron, exon
C. cistron, exon
D. exon, cistron

Answer

To solve the question regarding the coding and non-coding sequences of DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- **Coding Sequence**: This refers to the part of the DNA that is transcribed into mRNA and eventually translated into a protein. In eukaryotic cells, this is represented by **exons**.
- **Non-Coding Sequence**: This refers to the segments of DNA that are not translated into proteins. In eukaryotic cells, these are known as **introns**.

2. **Identify the Options**:
- The options given are:
a. Exon-intron
b. Intron-exon
c. Cystron-exon
d. Exon-cystron

3. **Analyze Each Option**:
- **Option a (Exon-intron)**: This indicates that the coding sequence is exon and the non-coding sequence is intron. This aligns with our definitions.
- **Option b (Intron-exon)**: This suggests that the non-coding sequence comes first, which is incorrect.
- **Option c (Cystron-exon)**: The term "cystron" is not commonly used in this context and does not represent a standard classification.
- **Option d (Exon-cystron)**: Similar to option c, "cystron" is not a recognized term for non-coding sequences.

4. **Select the Correct Answer**:
- Based on the analysis, the correct representation of the coding sequence (exon) and the non-coding sequence (intron) is found in **option a: Exon-intron**.

### Final Answer:
The correct option that represents the coding sequence of DNA and the non-coding sequence of DNA, respectively, is **a. Exon-intron**.