Final answer:
Genes are located in the DNA of a one-celled organism.
Step-by-step explanation:
The location of genes in a one-celled organism would be in the DNA, labeled as 'DNA' in the diagram. DNA, also known as the genetic material, is responsible for storing and transmitting the organism's genetic information, including the genes. Genes are segments of DNA that contain instructions for the synthesis of proteins and are essential for the organism's traits and functions.