02-07-2013, 01:30 PM
I just learned about this gene which is called Sonic the Hedgehog Homolog. It is a gene that deals with the development of facial features during the embryonic stage. Someone with an excess of this gene gains Diprosophus which causes the person to grow two faces. This happens a lot in cats and are known as "Janus Cats" named after the two faced Roman god Janus.
http://en.wikipedia.org/wiki/Diprosopus
http://en.wikipedia.org/wiki/Sonic_hedgehog
http://en.wikipedia.org/wiki/Diprosopus
http://en.wikipedia.org/wiki/Sonic_hedgehog