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This little fellow is named Buddy and he's believed to be a Chihuahua mix. It seems quite possible to me that he's just a big purebred Chihuahua, as is commonly seen in those bred to be pets. Though he's merle, this color is not unknown in the breed, and is perfectly acceptable according to the AKC standard. So, what's his genotype?
To begin, he is tan pointed. Though faint, the classic markings seen on tan pointed dogs are present. This makes him atat tan pointed.
Buddy is also liver, since he clearly has brown pigment rather than black. As with all liver dogs, this makes him bb liver.
The red in his coat is also quite pale, which explains why the tan points are so difficult to see. Going with the theory that the Chinchilla locus controls red intensity, this would make him cece very pale red.
Next, Buddy is most definitely merle. He's actually a fairly pale merle, with the lighter merle patches being similar in intensity to his tan points. He doesn't show any signs of being a double merle, so this means he must be Mm merle.
Lastly, this Chihuahua has white markings. They can be seen on all four paws and on his face, but it is difficult to tell since he's overall so pale. The markings fit in with what's to be expected from the Irish white gene, so he's most likely sisi Irish white.
So, that's atat bb cece Mm sisi or liver merle with pale tan points and Irish white.