Diverse evolutionary rates and gene duplication patterns among families of functional olfactory receptor genes in humans

Abstract

In humans, odors are detected by ~400 functional olfactory receptor (OR) genes. The superfamily of functional OR genes can be further divided into tens of families. In large part, the OR genes have experienced extensive tandem duplications, which have led to gene gains and losses. However, whether different OR gene families have experienced distinct modes of gene duplication has yet to be reported. We conducted comparative genomic and evolutionary analyses for human functional OR genes. Based on analysis of human-mouse 1-1 orthologs, we found that human functional OR genes show higher-than-average evolutionary rates, and there are significant differences among families of functional OR genes. Via comparison with seven vertebrate outgroups, families of human functional OR genes show different extents of gene synteny conservation. Although the superfamily of human functional OR genes is enriched in tandem and proximal duplications, there are particular families which are enriched in segmental duplications. These findings suggest that human functional OR genes may be governed by different evolutionary mechanisms and that large-scale gene duplications have contributed to the early evolution of human functional OR genes.

Fig 1. The human functional OR genes evolved relatively faster than the genome average.

Comparison of Ka (A), Ks (B) and Ka/Ks (C) between human functional OR genes and the rest of the genes in the human genome”.

Fig 2. The human functional OR genes tend to have a higher Tajima’s D than the genome average.

Comparisons of Tajima’s D between functional OR genes and all genes in the human genome. (A) In AFR. (B) In EUR.

Fig 3. Different evolutionary rates and selection patterns among families of human functional OR genes.

(A) Comparison of Ka. (B) Comparisons of Ka/Ks. (C) Comparisons of Tajima’s D in AFR. (D) Comparison of Tajima’s D in EUR.

Fig 4. Evolutionary relationships between human and outgroup species.

A dendrogram illustrating the evolutionary relationships of functional OR genes between the indicated species.

Fig 5. Families of human functional OR genes significantly differ in the number of syntenic genes in the outgroup species.

Comparison of numbers of syntenic genes in outgroups species among families of human functional OR genes. The comparison was statistically significant (P = 1.42×10⁻³⁰) based on Kruskal–Wallis test.