Define gene.

Explanation

**Step-by-Step Solution:**

1. **Definition of Gene**: A gene is defined as the basic physical and functional unit of heredity. This means that genes are the fundamental units that carry genetic information from one generation to the next.

2. **Composition of Gene**: Genes are made of DNA (deoxyribonucleic acid). This indicates that the genetic information is stored in the sequence of nucleotides that make up the DNA.

3. **Location of Gene**: A gene is located at a specific position on the DNA strand. This specific location is where the gene can be found and identified.

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