A segment of DNA that contains the instructions for building a specific protein or functional RNA molecule.

Here's why:

* DNA: Genes are made up of deoxyribonucleic acid (DNA), the molecule that holds the genetic code of an organism.

* Instructions: Genes contain a sequence of nucleotides (A, T, C, G) that act like a blueprint for creating a specific product.

* Protein or RNA: Most genes provide instructions for making proteins, which are the workhorses of the cell. However, some genes code for functional RNA molecules, which have roles in regulating gene expression and other cellular processes.

In simpler terms: Think of a gene as a recipe for a specific protein. The recipe is written in the DNA code, and the protein is the final product.

Important notes:

* A single gene can be involved in multiple processes.

* Many genes work together to create complex traits.

* Genes can be turned on or off depending on the needs of the cell.

Let me know if you have any further questions!