Genes control variation by coding for certain traits inside an organism. Those codes are adenine, cytosine, guanine and thymine. All of these four codes are acids and these acids depends on the variation within a species. This is how it makes an organism change the way it look physically. The four simple coded message codes for everything like eye color to height.
Genes codes for many traits and they are important in evolution of a species. Individuals in a species will have genes that will code for traits and therefore, will give them an advantage in the environment that they live and would lead them to reproduce more and there will be a great number of theses species