So why cross breed? Are The puppies healthier? When the parent dogs don't share the same known genetic health issues the percentage of cross breed dogs with genetic problems is MUCH lower than purebred dogs because the gene pool is mixed.

There are SEVERAL genetic issues that are shared by the Shih Tzu and Yorkie.

Here is a list of SOME health issues known in the Shih Tzu and YORKIE Breed.

Liver-Portosystemic Shunt

Knees-Patellar Luxation

Retinal Dysphasia - Eye Problem

So when doing a F1(first generation) or F2 or even F3, you need to make sure your breeder is doing genetic testing, so the chance of the parents passing any of these's issues to their off spring is very low to none.

 Hetaerists effect and hybrid vigor. Vigor means, "Physical or mental strength, energy, or force."

ONLY works with genetic issues that are known in only one of the parent breeds. This does not work with issues in both breed. For these's issues it is like breeding purebred to purebred. 

 

 

To help you understand the concept we here is an example:

 

 

F1 = 1st generation puppy - 50% purebred-A and 50% purebred-B - for example, a Yorkie to Shih tzu, this is first generation.

F2= 2nd generation puppy - shorkie to shorkie for the first time

 

1st generation 2nd generation