Factors in Heredity are determined by genes, which are the basic units of heredity. Genes are made up of DNA and are responsible for passing on traits from parents to their offspring. Genes are responsible for determining physical characteristics such as eye color, hair color, and height, as well as other traits like intelligence and personality. Genes can be passed down through generations, and can be modified by environmental factors. Understanding how genes work is important for understanding how traits are inherited and how diseases are passed down.