Classified as the same breed:
Poodles (standard, miniature and toy), Manchester Terriers (standard and toy), Xoloitzcuintli (standard and toy (I think??)), American Eskimo Dogs, Beagles, Portugese Podengo (Pequeno, Medio, Grande), Dachshunds (Miniature and Standard)
Classified as different breeds (by AKC):
Greyhound and Italian Greyhound (and possibly whippet), Bull Terrier and Miniature Bull Terrier, Large Munsterlander and Small Munsterlander
I think that's it. Note that I'm NOT including breeds that were outcrossed to get a smaller version. Only ones that I'm pretty sure came from selectively breeding for sizes. Also, I may have forgotten some.







