Most of the nutrients in a potato are in the peel.
Yukon Gold/ Klondike Gold and Russet potatoes are more closely related than sweet potatoes.
I think white fleshed potatoes are descended from potatoes originating in Peru. There are hundreds of varieties of potatoes in Peru. There are a lot of varieties of sweet potato as well. I think that most of these originated in Mexico, but Indians in the Southern US were raising them when the White men arrived. The Mexican word is camote, and these are similar to what Americans call sweet potato and yam. In Spanish the usual word is batata. In Spain they are called boniato, but what is sold under that name here in Miami is different. I think that sweet potatoes are also native to parts of South America as well as North America, as they are popular in Argentina and Paraguay.
Sweet potatoes are called yams, but a true yam (?ame) is a large root vegetable with white flesh. There is a lot of confusion with regard to the names of potatoes, cassava, yams, yautia and such. Sweet potatoes are much more nutritious than white potatoes, and are only distantly related to them. Check out Wikipedia (in both English and Spanish) for details. I do not claim to be an expert.