While making this mod, I tried to find a balance between implementing a deep and satisfying gene system and keeping traits as common as they are in vanilla. One way this was achieved was by creating a new tier for the 4 primary trait groups (intelligence, strength, attractiveness, and height.) The lowest tier in these groups is merely a mild buff, the other tiers are kept around as rare as they were in vanilla. The numbers I've used were selectively chosen to make sure traits don't become too common. For example, in the intelligence group:

Geniuses should be 0.6% of the population (rarer than vanilla)
Quick should be 2.4% of the population (more common than vanilla)
Bright should be 7% of the population

You should see more traits, but the majority will be low tier traits with smaller impact.

Overall, the chances of a child inheriting a trait in this mod are higher than vanilla - where a large percentage of congenital traits were birth mutations.

In vanilla a genius parent and a non-genius parent have a 15% chance to pass the genius trait down.

Here its not anywhere near as simple. A genius parent either has six alleles (AABBCC) or 5 (AABBCc or some variant of that.) The non-genius parent could have any allele pattern - though most likely 2-4 alleles. If she has 3, then you can get either 3,4,5 or 6 alleles for your kids. And in each case, there is a different genotype to phenotype conversion. If you have 6 alleles you are almost guaranteed to get genius, quick, or bright. If you have 5 you are less likely but still a good chance. For 4 alleles it's rare and for 3 they won't get the traits.

Notice the implications of that! A character could have aabbcc but NOT be an imbecile. The best way to check if someone's genes are good is not be looking at their traits, but the traits in their family!