|MadSci Network: Development|
Back in my teaching days, I used to have a great slide that I would use for my embryology classes. I got it from the front page of The Star, a tabloid newspaper. The caption for the photograph was "Doctors Stunned by Birth of One-Eyed Baby", and the picture was a mostly normal-looking baby with his eyes airbrushed out of the photograph and a totally fake looking picture of an eye pasted to his forehead. It was always good for a laugh. This condition does exist in real life in both animals (as you have seen) and humans, and it is called cyclopia. Real-life examples don't look anything like they do in the comics or sci-fi movies - check out the link for some examples - www.seatopia.com/miscellania.html [Not for the squeamish - Moderator]. Cyclopia in humans and animals is probably the most severe manifestation of holoprosencephaly, which is a defect in brain development in the early embryo. In mild cases of holoprosencephaly, brain development is nearly normal and there are few or no obvious facial deformities. In cases severe enough to cause cyclopia, the brain is so defective that the baby is either stillborn or dies soon after birth. The causes of cyclopia and holoprosencephaly are mainly unknown, although clues are being discovered. There are studies indicating that part of the cause may be a defect in how the embryo uses cholesterol during development. A gene that may be involved in holoprosencephaly has also been identified - it's called, believe it or not, Sonic hedgehog (yes, after the video game character - it was discovered originally by fruit fly geneticists and they often have a strange sense of humor). Here's another link to an article describing some of this research - http://www.niehs.nih.gov/centers/1998news/ctrnews9.htm
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