Of SNPs and Smells

The language of a DNA sequence is more than meets the eye. A string of A, C, T, and G can indeed encode a string of amino acids. At a higher level, however, nuances of sequence may impart evolutionary information, because variants accumulate over time. Single nucleotide polymorphisms--SNPs--for example, are scattered throughout the human genome on average about one every 500 to 1,000 DNA bases. But they are not distributed evenly, and their clustering or paucity may hold clues to the past. A team of researchers from the Crown Human Genome Center at the Weizmann Institute of Science in Rehovot, Israel, is analyzing SNP patterns to paint a portrait of the evolution of the human sense of smell.¹

This sense derives from an inch-square patch of epithelium high in the nasal cavity. Here, some 500 types of olfactory receptor proteins bind different combinations of odorant molecules. The bending sends...