Half Aliens and Aliens?

Hi, I'm thinking of trying to create a Sim with as many ancestral traits (Ancient Bloodline, Sulani Mana, and Father Winter's Baby) who also has as many occult types as possible (Vampire-Spellcaster-Mermaid-Werewolf-Alien). I'll probably use a mod to fix the glitchy-ness from hybrid sims, but I noticed that Aliens were a bit different from the other occults. For Vampires, Spellcasters, Mermaids, and Werewolves, the Sim seems to either have these occults types or not have them, but for Aliens, there is the option to have a Half-Alien. And I was curious, is there a way for me to have a full-alien child with a non-alien Sim (like another Occult or Father Christmas)? Or are Half Aliens only possible? And if Half Aliens are only possible, does the alien gene go away after a certain amount of generations? Are there Quarter Aliens? Any help is greatly appreciated!