Heritable differences in chemosensory ability among humans

Humans use several kinds of information to decide what to eat, and the combination of experience and sensory evaluation helps us to choose whether to consume a particular food. If the sight, smell, and taste of the food are acceptable, and we see others enjoying it, we finish chewing and swallow it. Several senses combine to create the idea of food flavor in the brain. For example, a raw chili pepper has a crisp texture, an odor, a bitter and sour taste, and a chemesthetic ‘burn.’ Each of these sensory modalities is associated with a particular group of receptors: at least three subtypes of somatosensory receptors (touch, pain, and temperature), human odor receptors, which respond either singly or in combination; [1,2], at least five types of taste receptors (bitter, sour, sweet, salty, and umami (the savory experience associated with monosodium glutamate [3])), and several families of other receptors tuned to the irritating chemicals in foods, especially of herbs and spices (for example, eugenol found in cloves [4] or allicin found in garlic [5]). The information from all these receptors are transmitted to the brain, where it is processed and integrated [6]. Experience is a potent modifier of chemosensory perception, and persistent exposure to an odorant is enough to change sensitivity [7].Each person lives in a unique flavor world, and part of this difference lies in our genetic composition, especially within our sensory receptors [8]. This idea is illustrated by bitter perception and bitter receptors. The bitter receptor family, TAS2, has approximately 25 receptors, found at three locations in the human genome [9,10]. We say ‘approximately’ because bitter receptors have copy number variants [11], and it is currently unclear at what point a recently duplicated gene should be assigned a distinct name. This conundrum is more than a mere matter of record-keeping; the bitter receptor gene copy number is a source of biological variation and may affect perception, altho