Here's why:

* Structure: DNA is a long, complex molecule made up of two strands of nucleotides that are twisted together in a double helix. Each nucleotide contains a sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

* Genetic Code: The order of these bases, known as the genetic code, determines the sequence of amino acids in proteins, which in turn determine the traits of an organism.

* Inheritance: DNA is passed down from parents to offspring, ensuring the transmission of genetic information.

While there are other chemicals involved in the process of gene expression, like RNA, DNA is the primary molecule responsible for transmitting traits.