Inheritance units are the genetic material that is passed from parent to offspring. Genes are the basic unit of heredity, and they are composed of DNA. They contain the instructions for the development and functioning of an organism. Genes are responsible for the physical characteristics of an organism, such as eye color, hair color, and height. They also determine the risk of developing certain diseases. Inheritance units are passed down from generation to generation, and they are responsible for the similarities and differences between individuals.