Most of Philip K Dick's works aren't hard Sci-Fi in the least. Philip K Dick usually focused on philosophical problems like identity and the nature of reality, rather than on technical details.
I've read "Do Androids Dream of Electric Sheep", and there is little mention of genetics in the novel. Keep in mind that the novel and the movie only share a few common scenes and plot threads.
The movie itself doesn't go into any great detail about how the androids are constructed. We are told that the creators of the fake lifeforms can leave their signature on the scales of a pet snake.