Final answer:
The Welsh Corgi is the dog breed with Pembroke and Cardigan variations. Domestic dogs can interbreed across different breeds, as demonstrated by the cockapoo, a mix between a poodle and a cocker spaniel. Labrador retriever coat colors exhibit genetic epistasis controlled by E and B alleles.
Step-by-step explanation:
The dog breed that comes in two variations, Pembroke and Cardigan, is the Welsh Corgi. Despite the physical distinctions that lead to the classification of these breeds, domestic dogs (Canis lupus familiaris) are capable of interbreeding across varieties, as their differences are phenotypic. These differences can include size, build, and coat, but most dogs are biologically capable of mating and producing viable offspring, not limited by breed appearances.
Those interested in dog breeding practices may reference how the poodle and cocker spaniel can interbreed to produce a hybrid known as a cockapoo, as shown in Figures 18.9 and 18.10. This is evidence of the extensive interbreeding capabilities within the dog species, regardless of the breed distinction.
Other examples of biogenetics in dogs include the fascinating case of Labrador retrievers, where fur color is controlled by alleles, E and B. This demonstrates an instance of epistasis where various combinations of these alleles dictate the resultant color of a Lab's coat.