Golden retrievers typically have straight tails, but certain genes can cause the tail to curl. Mixed-breed dogs can inherit genes from both parents, so if a golden retriever is crossed with a dog that has a curled tail, the resulting puppy may have a curled tail as well.
The shape of a dog's tail is primarily determined by the vertebrae in the tailbone. Some dogs have more vertebrae in their tails than others, and this can affect the shape of the tail. Dogs with longer tails tend to have curlier tails than dogs with shorter tails.
The length and shape of a dog's tail can also be influenced by environmental factors, such as how the dog is handled as a puppy. If a puppy's tail is constantly pulled or bent, it may become curled.
So, while it is not common for a golden retriever mix puppy to have a curled tail, it is possible.