When I began my Royal Legacy Challenge, I made one rule for myself. I would not allow any members of the Four main families to marry any one other then members of the Four main families. This was relatively easy, seeing as they all had blue skin, 'a true blue blood trait'.
But as the legacy began to unfold, I started to understand the genetics of the Sim 3 game.
It all began with the Hidden Trait, French Culture. When I started the Royal Legacy, there was only five sims with the trait, and they all belonged to the same family. They were the Simbons, the Royal Family of SimFrance. As pertaining to my 'blue blood rule', the King Gaston and Queen Marie-Leann's four children were married into the various Royal Families of the Known SimWorld. Princess Marie-Sophie married Supreme Duke Theodore of All Sims, Princess Marie-Belle married Crown Prince Hugo Vanderburg of Hidden Springs, and Princess Marie-Jose married Emperor Leon Simaparte of the SimFrench. The heir to the throne, Dauphin Remelle Simbon was married to Princess Supreme Merrywythyr of All Sims. But interestingly enough, I realised that the French Culture trait was passed mostly to the four Royals female offspring if they only their mother had the trait, and only to the son if the father had the trait. Even more curious, if both parents possessed the trait, then only two out of three of the offspring would have the trait, and it was very rare that the firstborn recieved it.
My second experiment was conducted with the Genie trait. Again, the female offspring were more likely to recieve the trait than the males. This time, if both parents had the trait then it was a 100% chance that the offspring will get it.
Furthermore, each family seemed to have a dominant trait that remained with their direct descendants.
I'm only up to the thirteenth generation, so more genetic discoveries AWAIT!