Here's why:

* Genes are segments of DNA: Genes are specific sequences of nucleotides within the DNA molecule that code for a particular protein or functional RNA molecule.

* DNA is organized into chromosomes: In most organisms, DNA is packaged into structures called chromosomes. Each chromosome contains many genes.

* The number of genes varies: The number of genes in an organism's genome can vary greatly. Humans have approximately 20,000 genes, while other organisms can have significantly more or fewer.

Therefore, a single DNA molecule, especially within a chromosome, contains many genes.