I found this a few days ago and it's just too fascinating to not share. I recently discovered something called Sonic Hedgehog protein
in my never-ending wikipedia adventures on metabolism/biochemistry. Yes, that is it's actual name, which is AWESOME. It's involved in patterning; i.e. formation and designation of size/shape of organs and various body parts. It's the reason why a fertalized egg doesn't just endlessly develop into a sphere of cells.
As you'd imagine SHH protein, and others like it are essential to life, and defects can cause fatal problems. One such problem that it can cause, is something known as holoprosencephaly
, which is when the brain fails to divide into two parts. There's varying degrees of it, but more severe cases can cause severe and fatal mutations.
Such as this, a live newborn with a single eye, and no nose. Aka, the baby is a literal cyclops. It's creepy, but also SO fascinating considering what causes it: