Olfactory Receptor Genes: Evolution

Abstract

Abstract Many mammal genomes have approximately 1000 genes encoding olfactory receptors (ORs), and OR genes constitute the largest multigene family in mammals. Comparisons among the OR gene repertoires in a broad range of species demonstrates that gene duplication and pseudogenization cause frequent gene gain and loss in this family, causing drastic evolutionary changes in the number of genes depending on species' ecological niches and other sensory modalities. For example, higher primates are equipped with a well‐developed visual system, and they have a reduced OR gene repertoires relative to mammals with lesser visual systems. Additionally, aquatic and terrestrial vertebrates retain different sets of OR genes, and these sets reflect the capacity to detect water‐soluble and airborne odorants, respectively. The origin of vertebrate OR genes can be traced back to the common ancestor of chordates, but insects and nematodes each use a distinct family of genes to encode chemoreceptors; therefore, multiple distinct chemoreceptor gene families emerged independently during animal evolution. Key Concepts: Olfactory receptor (OR) genes are the largest multigene family in mammals. OR gene repertoires changed dynamically during mammalian evolution and these changes depended on each species' ecological niches and other sensory modalities. Distinct chemoreceptor gene families have emerged independently multiple times during animal evolution. Comparative evolutionary analysis of OR genes provides insights into the interactions between genomes and environments.