Final answer:
Jacob had twelve sons, who were the ancestors of the twelve tribes of Israel. While there are technically thirteen tribes because of Joseph's sons, they are collectively referred to as the twelve tribes.
Step-by-step explanation:
Jacob had twelve sons in total. These sons are significant in the context of Biblical history because they became the patriarchs or fathers of the twelve tribes of Israel. Each son became the ancestor to one of the tribes. However, when considering the mothers of these sons, there is an interesting note: Joseph, one of Jacob's sons, had two sons, Ephraim and Manasseh, who were each the forebear to a tribe.
Thus, technically, while Jacob had twelve biological sons, there are thirteen tribes because of Joseph's two sons, but still, they are collectively referred to as the twelve tribes due to the tradition of combining Joseph’s descendants into one tribe or substituting one of his sons in his place.