Define Cistron.

Explanation

**Step-by-Step Text Solution:**

1. **Definition of Cistron**: A cistron is defined as a structural gene. It is a specific segment of DNA that carries the information necessary to produce a polypeptide.

2. **Function of Cistron**: The primary function of a cistron is to encode for a polypeptide, which is a chain of amino acids that forms proteins.

3. **Difference Between Cistron and Gene**: While both cistrons and genes are segments of DNA, the distinction lies in their specific functions. A gene can encode for RNA or proteins, whereas a cistron specifically encodes for a polypeptide (protein).

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