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  • I am a sun sneezer. Which is also known as having the photic sneeze reflex

  • Or, the autosomal dominant compelling helio ophthalmic outbursts syndrome.

  • Which basically means if I go from a dark area into somewhere that's brightly lit - You know, like, looking at the sun - I will sneeze.

  • Wait for it...

  • There you go, I'm a sun sneezer.

  • But why does this happen?

  • People have known about this effect for at least a few thousand years

  • Aristotle was probably a sun sneezer because in his book of problems

  • he asked: Why does the sun provoke sneezing?

  • And his answer was it was the heat from the sun which causes

  • sweating inside your nose, and so you sneeze to get rid of the moisture.

  • but a couple millennia later

  • Sir Francis Bacon demonstrated that this could not be the case because when he closed his eyes and turned towards the sun

  • well he did not experience that photic sneeze reflex so his explanation was that it was the eyes

  • watering and then when some of that moisture got down into the nose that caused the tickle which makes you sneeze

  • but even this theory has its problems because eye watering is a much slower process than the photic sneeze reflex

  • So it can't be the cause. Before I started researching sun sneezing

  • I thought that having the photic sneeze reflex

  • Must Convey some sort of evolutionary advantage under the people who have it. If you think about it

  • Sneezing is a way of transmitting disease. In your snot there can be the living Bacteria that cause

  • Tuberculosis, and strep throat or viruses that cause measles mumps Rubella and influenza, so if you're living in a moist dark cave

  • and you sneeze

  • Where your snot lands on the floor or the walls of the cave and those Pathogens can stay alive for hours or even days

  • increasing the Likelihood of spreading that disease to other people who live with you in your cave

  • Whereas if you only sneeze when you emerge from the darkness of the cave and into bright sunlight

  • Well, then that mucus will quickly dry out or because it's exposed to the harmful UV rays of the sun

  • It will kill all of those pathogens

  • Greatly decreasing the risk of spread of disease

  • By the 1960s some studies were revealing the hereditary nature of the photic sneeze reflex

  • There was a father who would sneeze two times when he entered bright sunlight

  • And when they tested his baby daughter who was just four weeks old

  • Moving her from a dark room into full sunlight also caused her to sneeze

  • Exactly two times and by the 1980s it was clear that this trait was

  • autosomal dominant

  • Meaning that you only needed to inherit one

  • Copy of the Gene from just one of your parents in order to exhibit the trait

  • But when studies the population have been done only about 18 to 35 percent of people actually have the photic sneeze reflex

  • So I don't really think this gives a great evolutionary advantage, otherwise everyone would have it

  • you know it could just be one of those random mutations that happens over time and

  • Sustains itself because it's neither good nor bad evolutionarily speaking

  • So it affects roughly one in four people

  • Can you spot the person with the photic sneeze reflex?

  • Nowadays, it's actually been found that the gene responsible for the photic sneeze reflex is on the second chromosome

  • And it's a single letter of DNA that's been changed, on my second chromosome

  • I have a C

  • Where non sun sneezers have a T, and the reason that we know this is that back in 2010 there was a study of about

  • 10,000 people where they went online and they

  • Reported whether they were sun sneezers or not and then their DNA was

  • analyzed and the groups were compared and what they found was the thing the sun sneezers had in common was this one particular

  • letter change in their DNA.

  • That I think is pretty amazing.

  • Now it's unclear exactly how this change affects your physiology and makes you more susceptible to sun sneezes

  • But the best theory at the moment is that it involves the trigeminal nerve which is the largest cranial nerve it

  • Involves all of the feeling that you have in your face and as the name implies

  • It actually has three branches one of which receives stimuli from your eye and another which receives stimuli from your nose

  • so the thought is that this really active stimulation of the optic nerve may cross over into the

  • maxillary Branch causing that little tickle which gets you to sneeze

  • Photic Sneezes are generally pretty harmless unless you're doing something like flying a fighter jet or performing some sort of delicate surgery.

  • But this methodology,

  • can allow us to learn a lot about different heritable traits and diseases just by studying lots of people and their genotypes

  • This episode of veritasium was supported by 23andme. Which is actually the company that figured out that gene polymorphism

  • responsible for the photic Sneeze reflex

  • the name of the Company 23andme comes from the fact that humans actually have 23 pairs of chromosomes and

  • The purpose of the company is to give people insight into their own DNA

  • So what you do is spit into a vial

  • which is actually much harder than it sounds and

  • Send it off to them and of course in your saliva are some of the cells from your mouth

  • They analyze the DNA from those cells

  • And then they send you a report where you can find out tons of stuff about your genes like

  • Where do your genes come from that is what's your ancestry and do you have the photic sneeze reflex? Do we share the same?

  • Change of DNA on our second chromosome you can also learn about your health and other physical traits and how much

  • Neanderthal you are so if you want to learn more about your genotype

  • Then you should go to 23andme.com/veritasium, so I want to thank 23andme for supporting me

  • And, I want to thank you for watching.

I am a sun sneezer. Which is also known as having the photic sneeze reflex

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B2 中高級

太陽打噴嚏的基因 (The Sun Sneeze Gene)

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    林宜悉 發佈於 2021 年 01 月 14 日
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