Being chosen to be possesses by a god is the highest honor an individual can receive in this world religion. The person has their soul subsumed by the deity, becoming one with them. The resulting demigod emerges as an entirely different being, who gains access to the god's abilities on the mortal plane. This being lives for 1000 years, in which he heads his community as a tribal leader. After this timeframe, this demigod ascends to the heavens and returns to the god realm. After some time passes, a new individual is chosen for this ritual to be possesses by that same god.
While this demiogd is one earth, he or she can produce children. These descendents are the only ones who can undergo the ritual to be possessed by that god.There can be only one demigod at a time, and there are several clans like this in existence. However, descendents of these clan don't gain any magical or godlike abilities unless they are chosen. There is no change in their genetic structure or alterations in their biology to make them any different from other mortals.
Since their are no genetic structures that separate this clan from other mortals, what can I use differentiate them from other humans to make them capable of being possessed in this way?