Through the 200 years since the Great War, dogs have remained relatively unaltered by radiation.
Dogmeat for example, is a German Shepherd dog that may be a companion to the Sole Survivor. There are a few different distinct breeds of dogs. Some mongrels will attack on sight but can be pacified. Before the war many of them had fur, but now many of them have lost it and their pink skin is visible. Humans and super mutants are the only species known to truly tame and domesticate these canines. There are also rare cases of domestic breeds that act as companions towards their bipedal counterparts.
Some dogs are wild, plaguing the wastes and killing livestock, but tame versions are necessary for many struggling wastelanders.