Most modern dogs have wolf DNA

Most modern dog breeds have small amounts of wolf ancestry from long after dogs were domesticated. The wolf DNA isn't left over from when dogs and wolves diverged; instead, it most likely came from interbreeding in the past few thousand years.

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That wolfish influence may be linked to certain characteristics, such as size and personality traits, in different dog breeds, researchers reported in the Proceedings of the National Academy of Sciences. Wolves and dogs genetically split more than 20,000 years ago. Since then, there has been some gene flow between dogs and wolves thanks to their genetic compatibility. To measure the extent of intermixing and its effects on both animals, researchers studied the previously published genomes of nearly 2,700 dogs and wolves from the Late Pleistocene (the last ice age) to the present. This group included 146 ancient dogs and wolves, 1,872 modern dogs and about 300 ‘village dogs’ that lived around humans but weren't pets.