Explaining the Cake family's geneticsTitle: A dissertation on the hypothetical genetics of the Cake family
There has been dissension among the ranks of bronies as to whether the Cake parents, who are Earth ponies, could produce a pair of fraternal twins with one being a pegasus and the other a unicorn, given only one distant ancestor carried a single representative phenotype of each on either side.
I have developed a plausible pattern of inheritance to explain this seeming incongruity.
Let's say that pegasi and unicorns were genetically designed, using earth pony as the genetic base, by the alicorns playing god on the mythical continent of Atlantis. The easiest way to add the genes to the earth ponies would be to design an artificial chromosome carrying all the needed genes. Then this chromosome's expression could be triggered by a special transcription factor integrated elsewhere in the genome, likely tied via a promoter to other developmental genes. My bet is the BMP-Bcat-Wnt