This is a short, clear, and fascinating video about the basics of genetic manipulation and, by extension, the use of engineering principles to create new organisms. As the squib says:
From selective breeding to genetic modification, our understanding of biology is now merging with the principles of engineering to bring us synthetic biology. Written, animated and directed by James Hutson, Bridge8.
Well worth the six minutes it takes to watch. If you cannot see the video, click here.