Petz inherit shape in parts. Which parent's (or grandparent, greatgrandparent, etc.) parts they resemble are fairly random, although they seem a little more likely to inherit from their parents and less likely to inherit from further back generations.
The groups of inheritance:
Head/Neck (all facial features, including the eyes, snout, etc.)
Arms/Legs (from shoulders to wrists and hips to ankles)
Hands/Feet (including fingers and toes)
Since they are grouped this way, it means that offspring cannot have the nose of one parents and the eyes of another, cannot inherit hind feet from a different parent than front feet, etc. Everything connected to these groups including relative size, position, ommissions, addballz, etc. This is why some mixes with hexed breedz result in extra or missing parts. If a tail is made of addballz and based off of the butt ball, it inherits as part of the body shape--not as a tail. (And why birdz sometimes end up with strange, unattached feet.) Within a breed that has variations, the inheritance groups are exactly the same, so if you breed a lion (with mane) to a lioness (without), some of the offspring will inherit the mane parts based off the chest but not those on the neck/head or vice versa.
Adult size is inherited from one parent or the other. But the ratio of adult to offspring is connected to body type, so if you breed a dog who's puppy form is much smaller than adult form to a dog with a small adult form, you can get very tiny puppies. The exception to size inheritance are hexed breedz that have been hexed beyond the game parameters. There are upper and lower limits to inheritable size, length, height, etc. Depending on the way a hexer accomplishes their goals, things do not always pass on correctly to offspring.
Eye size is limited by the size of the newborns, so very tiny newborns end up with big bug eyes.
To show some of the shape recombinations, below are some pictures below of crosses of very differently shaped (original) breedz. Notice the groupings of inheritance.
Here are the offspring (adult) of a Chihuahua x Sheepdog.
Here are the offspring (adult) of an Alley Cat x Chinchilla Persian.