Example of how taste and smell genotypes may contribute to the perception of common foods. A ham and cheese sandwich contains bread, onion, tomato, watercress, cheese, and ham. The low concentrations of sucrose in the onion will be detected by sweet receptors on the tongue, heterodimers of TAS1R2 and TAS1R3. The glutamate in the tomato, perceived as a savory or umami taste, is sensed by the umami receptor, which is a heterodimer of TAS1R1 and TAS1R3. The bitterness of watercress is due to isothiocyantes (or structurally related compounds) and is detected by one or more bitter receptors (i.e., TAS2R38). Isovaleric acid is a component of cheese and gives it a characteristic odor that some people call “sweaty.” This chemical stimulates at least one olfactory receptor, OR11H7. Ham can contain androstenone, which gives the meat an odor called boar taint. Some people perceive this odor as offensive, and the receptor associated with this compound is OR7D4. In this example, people with two positive alleles (+/+) perceive the compound better than people with two negative alleles (−/−). Person 1 can taste the pleasant sweetness of the onion and the umami of the tomato but does not perceive the bitterness of the watercress or the unpleasant odors of the cheese or ham. Thus, Person 1 likes the ham sandwich more than Person 2.