Smell is a very important sense for mammals; many people regard it as a fairly useless scent, but it has many, many uses. Flavor is highly dependent on smell, not to mention the ability to detect potential toxins, or to find compatible mates, smell is very important for everyday life. What makes smell fascinating is how complex the sensing is: where a sense like vision or touch need only a very small number of cells that are able to output at different strengths to produce a range of sensations, smell is reliant upon thousands of different receptors, each identifying one or multiple different smells for a total of 10,000 different smells.
The genes that code for this diverse smelling machinery make up the single largest family of genes, spread across many chromosomes. Despite their huge numbers, the individual genes are hard to trace back to a scent sensation, especially when you consider the huge variation in people’s tastes and sensitivities, which makes tracing difficult. All of this wasn’t enough to deter the New Zealand institute for Plant and Food Research, however, as they decided to launch a large-scale study of 187 individuals smelling 10 items well known for their scent, including blue cheese, apples, and violets. By monitoring their reactions, and comparing the data to the genetic sequences of the subjects, they definitively linked 4 of the smells to specific gene clusters. Considering that prior to the study there were only five such regions, this is a major milestone. The smell of violets was traced to a single gene, which enables or disables the ability to smell the flower, only two other smells are know to have this, a pig pheromone, and a compound associated with freshly cut grass, but many more are expected to be identified in the future.
The research also highlights the fact that each person had a different sensitivity to each compound, meaning that everyone experiences a different mix of sensations even when they are smelling the same thing. The team speculates that one day we will be able to tailor scents to people, accounting for all of their sensitivities to find the most pleasing smells. That they will be able to account for the memories that smells are associated with is less likely.
Identification of Regions Associated with Variation in Sensitivity to Food- Related Odors in the Human Genome – Current Biology
Smell isn’t exclusive to animals, plants also have the ability to detect airborne chemicals, including some parasitic plants, such as Dodder, that literally sniff out their prey.
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