Yo no tengo hermanos, solo tengo un que se llama Rico.

gata

hermano

perro

hermana

Perro

Explanation:

Yo no tengo hermanos, solo tengo un perro que se llama Rico.

I don't have siblings, I only have a dog named Rico/whose name is Rico.

Yo no tengo hermanos, solo tengo un perro que se llama Rico.

Explanation:

In this case the subject that is missing in the sentence is masculine, and since there are only two options, it is ruled out that he is a brother because at the beginning of the sentence he says that he does not have, then therefore it corresponds to the dog who is called Rico.