Out of all of the possible colors found with this breed, perhaps none is so dramatic as black and white (standard color, code S 019). The way in which color genes affect the coat makes it almost hard to believe that two opposite colors can present in this way.
In this section, we'll cover some facts about black and white Shih Tzu and then dive into some beautiful examples of both puppies and adults with this remarkable coloring.
Black and white Shih Tzu are not white dogs with black markings; they are black dogs with white markings, even if the black appears to be a secondary color. This holds true whether there is 5% black or 95% black.
When white appears on a black dog, this determined on the color genes by the S locus (spotting gene), in all cases except for extreme whites (mostly white and a bit of another color; in this case, black).
3) Though the S (spotting) locus is at play, this does not mean that a Tzu will literally have white spots; the gene produces varying amounts of white.
Though the piebald gene is only in play in black and white Shih Tzu with extreme piebald, piebald is
used to describe varying amounts of white on a black dog.
Parti-piebald - The Shih Tzu is about 50% black and 50% white.
Irish mark piebald - More black then white. White is often running over the forehead (blaze), the breastbone (brisket), chest, shoulders (shawl), tip of the paws and tip of the tail.
Extreme piebald - This is the one in which the S locus is not in play, but rather the piebald gene. The Shih Tzu will be majorly white with just a bit of black.
The spotting of white on black occurs while in the womb; it starts at certain places on a dog, this includes the paws, center of the chest, tail, muzzle and paws. Then, it spreads. How far it spreads is genetically predetermined.
The very last places that the white
spreads to is often the back (saddle) and the top of the head. For this reason, it would be extremely rare to see a white and black Shih Tzu with black just on the paws or just on the chest.
In regard to the spreading of that white (see above bullet point), the white will continue to spread over the black while the puppy matures. For this reason, when you have a black and white Shih Tzu puppy, most likely the patterns that you see will be different once he grows up.
Patches of color will not disappear in one spot on the body and appear in others; rather, the white (remember it is the white that changes, not the black) will spread.
So, if you have a Tzu with a bit of white on his chest at 8 weeks old, he can be an adult with a fully white chest. If a 12 month old has white paws, he may have fully white legs once he is done maturing, etc.