The Centauri Anthology

Remember, genes are NOT blueprints. This means you can't, for example, insert "the genes for an elephant's trunk" into a giraffe and get a giraffe with a trunk. There -are- no genes for trunks. What you CAN do with genes is chemistry, since DNA codes for chemicals. For instance, we can in theory splice the native plants' talent for nitrogen fixation into a terran plant.

Academician Prokhor Zakharov

Nonlinear Genetics