It's called "selection". If I want big red dogs, I select for the biggest and reddest puppies. You do that several generations and you'll get big red dogs.
Eventually we are going to be able to create a gene that gives us big red dogs starting off with rabbits or chipmunks. It really won't matter.
No human designed DNA. That is a fact. We can now engineer it and breeding is an indirect engineering, just like natural selection.
That is what Origin of Species is all about. Read it.