If you're among the one in four people who sneeze when you move from a dark place into the sunlight, this nifty little explainer from a fellow traveler gives a great overview of causation theories over the millennia. Turns out it is just one transposed letter in the second chromosome that causes the effect.
The dominant photic sneeze reflex trait gets passed on if one of your parents gives it to you. He clarifies his "sneeze gene" video title:
So technically the single nucleotide swap (C instead of T) is not actually in a gene per se but in an intergenic region on chromosome 2. It's also not clear exactly how this affects physiology or causes the sun sneeze but there is correlative evidence that every copy of this single nucleotide polymorphism (SNP) is associated with a 1.3x increase in likelihood of having the photic sneeze reflex.
• The Sun Sneeze Gene (YouTube / Veritasium)
