My favorite trait, and the one I’m quite thankful to have, is what’s know as the photic sneeze reflex. Sometimes called the Peroutka Sneeze Gene or even ACHOO syndrome (how droll), this reflex causes one to sneeze when exposed to bright light. I had always assumed everyone had this ability, but scientists estimate it affects 18 to 35 percent of the population. Try it out: the next time you need to sneeze but are not quite there, look out the window at the sun or at a light-bulb and if it pushes you over the edge then you have the phenotype! The photic sneeze reflex has intrigued great thinkers as far back as Aristotle. We still don’t know which gene is responsible for it, but we do know only one copy is needed, and it isn’t on either the X nor Y chromosome. How it works is still unexplained by science, but many experts now agree that crossed wires in the brain are the cause.

Here’s one you may have tested back in high school biology: The gene that detects the odor of cyanide. Do you remember your teacher passing around a vial and asking if you could detect a sweet almond smell? That’s what cyanide smells like to around 20 to 40 percent of the population. Studies have also found that men are less likely to smell cyanide than woman. About 18%-20% of men are not able to smell cyanide at all, whereas only 5%-10% of woman cannot. The rest of the population is able to detect the smell in significant quantities, but only 40% can smell it in trace amounts.

Quick, clasp your hands together! Now look down at your thumbs. Most people place their left thumb on top of their right one. Try clasping your hands so that the opposite thumb is on top and you’ll notice it doesn’t feel quite right. As random as it may seem, hand clasping with the left thumb on top is a dominant phenotype.

Do you have caveman fingers? Some people have hair on the second (middle) joint of one or more of their fingers. If you have hair on any of these middle joints then you posses the dominant phenotype. I was just kidding about the caveman thing–it doesn’t mean you’re less evolved, the absence of this hair is just based on a recessive allele.

Speaking of digits, next time you’re barefoot or in sandals, look at your second toe. If it’s longer than your big toe you have what is called morton’s toe (or sometimes “Greek foot”). Although this is a dominant genetic trait, it’s part of the genotype of only 10% of the world’s population (and can be a real hassle when sizing Five Fingers)!

There are many other common and observable phenotypes, but these are some of my favorites. To learn more about genetics check out Wikipedia’s series on the subject (be sure to scroll down to Related information at the very bottom).

Sources:

http://www.scientificamerican.com/article.cfm?id=why-does-bright-light-cau

http://en.wikipedia.org/wiki/Photic_sneeze_reflex

http://www.helium.com/items/1532959-human-genetic-traits-with-complete-dominance?page=2

http://en.wikipedia.org/wiki/Morton%27s_toe

“Sneeze” by wise.adam
“Green Poison” by ohsoabnormal
“sparkle Toes” by Robert S. Donovan
“Gravestone Sculpture 2″ by fallingribbons
“tiiiiiiiiiny camera, maaaassif lens” by Abulic Monkey

I came across this via Make:, but the source, and a great gallery of examples, is over at Noise Addicts.

It’s strange how well it works out, especially some they have posted. Here are three I did this morning (I could seriously make these all day):

Go try it out!