Here's where this started as support for the discussion of 'leg development'. The process of developing novel features through gene duplication and/or modification of regulatory genes has been reproduced in the lab. Please provide a relevant example where this did not result in a freak. No polyploidy in plants please. That wouldn't be relevant.
You made the claim that gene duplication always results in a "freak," or, a reduction in fitness for successive generations.
Can you support that claim with a reasoned biochemical and ecological argument or can't you?