The active odor receptor genes constitute approximately what percentage of the gene family?

The active odor receptor genes constitute approximately what percentage of the gene family?

• A. About 10%
• B. About 35%
• C. About 5%
• D. About 15%

Answer: (B)

Active odor receptor genes are the subset of the odorant receptor gene family that are actually expressed as functional receptors in olfactory neurons. The odorant receptor family is very large, but not all copies are usable; a substantial minority remain functional. Across species, the active fraction is about one-third, which makes sense given the need for broad detection of many odorants while many gene copies accumulate mutations and become nonfunctional over time. So the best match describes roughly a third of the gene family as active. The other options propose much smaller fractions that don’t align with the observed balance between gene family size and functional copies.

Active odor receptor genes are the subset of the odorant receptor gene family that are actually expressed as functional receptors in olfactory neurons. The odorant receptor family is very large, but not all copies are usable; a substantial minority remain functional. Across species, the active fraction is about one-third, which makes sense given the need for broad detection of many odorants while many gene copies accumulate mutations and become nonfunctional over time. So the best match describes roughly a third of the gene family as active. The other options propose much smaller fractions that don’t align with the observed balance between gene family size and functional copies.