The precise breeds are unknown, but it's thought the original dog was a mixed breed that occurred on the Shetland Islands, perhaps including spitz-type dogs—dogs with long, thick fur and pointed ears and muzzles—brought to the islands by the Scandinavians and Norse peoples who once ruled them. There is also an extinct breed called the Greenland Yakki which perhaps bore a resemblance to the first dogs in the Shetlands. By the 15th century more dogs from the Scottish mainland had arrived in the Shetlands, including Collies, with whom the Sheltie shares some of the same Border Collie ancestors. These ancestral Scottish herding dogs were bred with the local dogs in the islands; the term collie, in fact, is a Gaelic word meaning 'useful,' an apt term for this plucky little herding and guard dog.
No, the Sheltie is not a 'Miniature Collie,' even though it looks like a diminutive version of the Collie. Because Collies and Shelties share some ancestry, they do bear a resemblance to one another, and early versions of the Shetland Sheepdog were crossbred with Collies to refine them. But Shelties and Collies—two distinct breeds—developed independently of one another.
There is no such thing as a 'Miniature Sheltie,' and if a breeder claims to have them, they're merely breeding undersized Shelties to achieve a smaller dog. The AKC maintains standards for only one recognized breed, and that is the Shetland Sheepdog. If you want a smaller version of the dog, your best bet is to seek out a reputable breeder and choose the smallest pup in the litter.
Perhaps, with a little encouragement. Some Sheltie owners concede that their dogs absolutely hate water and refuse to fetch a ball tossed into it. Other Shelties appear to enjoy a cool dip on a hot day. Success in the water seems to boil down to early exposure to it, before nine months of age. And if your Sheltie can acclimate to it, swimming will be another way to keep him fit without stressing his joints, especially if he starts putting on weight as he ages.
In short, the Sheltie 'spin,' where he jumps and spins in tight circles like a top, is how he expresses excitement—you might call it joie de vivre, but many Sheltie owners simply call it the "zoomies." It is but one trait that makes this dog so endearing.