Can a fox and a dog mate?

In genus Canis (Dogs, wolves, jackals, and coyotes) the number of chromosomes is 78, no barrier to interbreeding exists in terms of chromosome segregation.There are some physical barriers due to size and behavior, which help maintain the separation of species in the wild. Not so with Canis vs. Vulpes. The question is not really whether species do interbreed, but whether they can interbreed under any conditions. Foxes, are out at ~8% sequence divergence, and only have 34 chromosomes, so a dog-fox hybrid probably is not viable.