@Mikezumi - No, I have never gender swapped or switched anyone. I take them as they come as exteriors are superficial and changable things to me which, in my humble opinion, has no importantance in what truly makes a sim who or what they are. That being stated, to my untrained eye, Mortimer resembles his mother despite their numerical values being different.
The 'Back in the Day' I was making reference to was in the vanilla base game timeline. The infants of that era all resembled the parent whom they were given to. I currently have a good number of them actively scattered throughout my various worlds. When these sims are toddlers, at first glance you can immediately see which families they were 'born' into as they all heavily resemble their single parent. However, as they become older, they develop into their own form as neither zero sliders nor clones of their parent. They are their own sim; this is how I would imagine Mortimers origin to be.