A person’s genome (the collective of all their genes) codes for proteins. These proteins include keratin (which makes up hair and skin) and melanin (which gives skin and hair their color). The bulk of the proteins, however, are enzymes, which catalyze specific reactions. These will regulate how much pigment is produced in your hair and skin, or how your nose develops, or where you store your extra fat, for example. When discussing this, the terms genotype and phenotype are often brought up. Genotype refers to the information held in the genetic code, phenotype is the observable trait.