@DivinylsFan - This is the first time I have ever heard of sims getting a new face. I haven't personally witnessed that; it could actually be a glitch who knows. When it comes to genetic understanding Mikezumi would be the best available source because it is their element of interest.
My interest lies in the AI elements of the game. The only place genetics and AI cross paths is under the umbrella of 'social events & learning'. Sims with facial features which are either too large, too small or disproportionately put together are at a social disadvantage purposely programmed in and enforced mostly through how the game's trait system works and its effects on what a sim learns. This does not affect actively played sims due to the fact the player controls the interactions, narratives and responses for their sim. Townies are not so lucky.
This isn't to say that a 'less-than-attractive' sim can't live a happy life, they can as long as they aren't saddled with traits which keeps them prisoners to the disadvantage (such as loner, inappropriate and the likes), anything which keeps them away from socializing and social learning.