Here's why:

* DNA is the genetic blueprint: It contains the instructions for building and maintaining an organism. These instructions are encoded in the sequence of nucleotides within the DNA molecule.

* Chromosomes are organized DNA: DNA is tightly coiled and packaged around proteins called histones to form chromosomes. This compact structure allows the long DNA molecule to fit inside the nucleus of a cell.

* Other components: While DNA is the primary component, chromosomes also contain a small amount of RNA and proteins. These play roles in gene expression and chromosome structure.

So, while chromosomes are complex structures, DNA is the core chemical that holds the genetic information.