All I can say is I never had a problem - I just accept what comes along. Then I changed my mind recently when I had a look at what I'd get when I paired up two of my sims. I got such a fright I operated on both of them immediately and make their faces much more alike.
I didn't get a screen shot of the scary monster but - dad had a short broad face and mother had a long narrow face. The result of their genetics that scared me had a short broad head from the eyes up and a long narrow head from the eyes down with a horizontal line below the parts of the wide top of the head that didn't have a corresponding part of the face immediately below it.
Since their plastic surgery in CAS they have produced some gorgeous children.
This pair just aged up to teen.
https://s5.postimg.org/ep28xo9cn/Leanne_Teen004.jpg
https://s5.postimg.org/4eztygtrr/Louise_Teen003.jpg
Although I can't claim the second of the two to be their own offspring exactly. I wanted her to turn out looking like this before I made the parents so when I got such a fright doing the play with genetics thing I changed the parents faces to more closely match her face. The reuslt was the sim at the top. Fortunately the pregnancy resulted in identical twins and I took the first born, seen here on the bottom, into CAS and changed her to make her look like the sim I was after originally. I had a particular story requirement for doing this otherwise I wouldn't have bothered.