Hidden traits

Hidden traits cannot be seen ingame except when a Sim performs the related action. They can only be acquired through genetics without mods. You can get these traits by having a baby with certain NPCs or a sim in a specific career. Your child will then get the appropriate hidden trait.

Burglar
''Burglars must perfect their sneaking skills to properly liberate imprisoned items from the homes of neighbors. Burglars like to keep the skill in the family, so their children are able to sneak out like a pro at birth.''
 * From NPC burglars and Sims in the Criminal career.
 * Can "Sneak" instead of walking or running.

Can Apprehend Burglar
''Police officers spend years to best the most clever burglars. Luckily for their children, genetics helps them stop burglars without years of tedious training.''
 * From NPC Police Officers and Sims in the Law Enforcement career.

Can Salute
Children of high-ranking military officials know enough about the military's rules and regulations to snap off a smart salute when they want.
 * From Sims in the Military career.
 * Can "Salute" other Sims.

Immune to Fire
''Fire Fighters are able to survive countless fires; not because of their natural immunity to fire. It's a trait that they pass on to their children.''

In Ambitions, children of Sims who reached the top of the Firefighter career will occasionally have this trait.

Makes No Messes
The descendants of maids have cleanliness imprinted on their genetic code so they never leave anything dirty.
 * From Maids.
 * Never leaves messes, similar to an attribute of the Neat trait.

Pizza Appreciator
''Pizza delivery folks develop a love of pizza that's deeper than the thickest crust. Their children share a similar fanaticism for pizza, which makes every bite of hot pizza amazing.''
 * Eating pizza grants them the Amazing Meal moodlet.
 * From pizza deliverer.

Pyromaniac
''You can only get this trait in a Sim who is the offspring of a firefighter Sim. The trait allows them to set fire to objects of their choice, and they get positive moodlets for doing so!''
 * From NPC firefighters and Sim firefighters at level 8+ of their career.
 * Can set fire to an apple and turn it into a flame fruit.

Rocker
Sims with this trait will get a natural feeling of rockstardom.
 * From Sims in the Music career.
 * Sims with this trait occasionally play air guitar.

Asian Culture

 * From Sims in Shang Simla.
 * Chinese-themed idle animations.
 * Uses chopsticks when eating.
 * Never get fatigued while practicing Martial Arts.

Egyptian Culture

 * From Sims in Al Simhara.
 * Sing Middle Eastern songs autonomously.

French Culture

 * From Sims in Champs Les Sims.
 * Sing French songs autonomously.
 * Greets other sims with a dual-cheek kiss.