The total number of odor receptor genes in humans is described as which magnitude?

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

Answer: (A)

Think about how many odor receptor genes humans have. The odor receptor gene family is very large, with estimates around 800 to 1000 genes in the human genome when counting both functional receptors and nonfunctional copies (pseudogenes). Roughly 400 of those are functional, with the rest being pseudogenes. Because the total sits in the hundreds to around a thousand, the right way to describe the magnitude is in the thousands. Describing it as millions would be far off, and billions or hundreds wouldn’t capture the full set. In other species, like mice, the family is even larger, which underscores how big this gene family is. So the total number is described as thousands.