Here's why:

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

* DNA is organized into chromosomes: DNA is packaged into structures called chromosomes within the nucleus of a cell.

* Chromosomes are visible during cell division: When a cell divides, the chromosomes become condensed and visible under a microscope.

So, while genes themselves are stretches of DNA code, they are physically located on and represented by chromosomes.