I was in an argument with a "vet nurse" in training and she told me that my Pure-bred Wire-haired Pointer won't be as healthy as cross-bred dogs on the count of that Pure-breds mutate every time they breed with their own species. "It's like their mating their cousins" is what she said. I'm open up to what she said but I don't believe her. I need this to be clarified please! Sources would be appreciated.