How many odor receptors do humans have?

How many odor receptors do humans have?

• A. Millions
• B. Thousands
• C. Hundreds
• D. Billions

Answer: (A)

The key idea is that smell is detected by a finite set of odor receptor proteins encoded by a large, but limited, family of genes. In humans, about 400 functional olfactory receptor genes are expressed, with many more copies existing as nonfunctional pseudogenes. That puts the functional receptor count in the hundreds, not in the thousands or millions or billions. The brain interprets smells by recognizing patterns of activation across these receptors, so having hundreds of receptors provides enough combinatorial power to distinguish a vast array of odors.

The key idea is that smell is detected by a finite set of odor receptor proteins encoded by a large, but limited, family of genes. In humans, about 400 functional olfactory receptor genes are expressed, with many more copies existing as nonfunctional pseudogenes. That puts the functional receptor count in the hundreds, not in the thousands or millions or billions. The brain interprets smells by recognizing patterns of activation across these receptors, so having hundreds of receptors provides enough combinatorial power to distinguish a vast array of odors.