For example, the creation of limbs and extremities is a higher order function of hox genes. you can take the hox genes that are responsible for creating a leg out of a squirrel, for example, and put them into a fly, and the fly will grow another leg. A fly leg.

So could this be used to modify human bodies? Regrow missing limbs, grow extra body parts etc? What about sex realignment, could someone swap their genitals using dna programming?