Quote from Siddhartha Mukherjee’s THE GENE on olfactory genes!

All you users of the scent test are going to love what Siddhartha Mukherjee writes in his amazing book, THE GENE. The only parts I have inserted are between square brackets [..] for clarity to identify the noun associated with the pronoun. The rest are all his words.
p. 323 “Parts of it [the genome] are surprisingly beautiful. On a vast stretch on chromosome eleven, for instance, there is a causeway dedicated entirely to the sensation of smell. Here, a cluster of 155 closely related genes encodes a series of protein receptors that are professional smell sensors. Each receptor binds to a unique chemical structure, like a key to a lock, and generates a distinctive sensation of smell in the brain — spearmint, lemon, caraway, jasmine, vanilla, ginger, pepper. An elaborate form of gene regulation ensures that only one door-receptor gene is chosen from this cluster and expressed in a single smell-sensing neuron in the nose, thereby enabling us to discriminate thousands of smells.”
p.325 “Its [The genome’s] first gene, on chromosome one, encodes a protein that senses smelling the nose (again: those ubiquitous olfactory genes!). Its last gene, on chromosome X, encodes a protein that modulates the interaction between cells of the immune system. (The “first” and “last”) chromosomes are arbitrarily assigned. The first chromosomes is labeled first because it is the longest.”