I once did a theoretical analysis of pony genetics. Another user had started, and I went deeper with it. I looked at all the basic traits and broke it down to the most basic set of trait genes to determine how unicorns, pegasi, earth ponies, and alicorns, as well as the potential for affinity to the elements of harmony go...
Two ponies were a single gene away from Celestia's genome.
Luna and Pinkie Pie.
I TOTALLY did not plan that.
By pure chance, that's where the genome fell. I was... shocked, and yet... not at all shocked!