Here's why:

* Genes contain instructions: Genes are segments of DNA that hold the instructions for building and maintaining an organism.

* Genes code for proteins: These instructions are used to create proteins, which carry out a vast array of functions in the body.

* Genes are fundamental: Genes are the fundamental unit of heredity, meaning they are passed down from parents to offspring.

* Genes are organized: Genes are arranged in a linear fashion on chromosomes, which are located within the nucleus of cells.

While there are smaller units within a gene, such as codons (sets of three nucleotides that specify an amino acid), the gene itself is the overarching unit that carries the genetic information.