I see three possibilities with elect angels as well as elect people. They are elect because of
1. something within them
2. something God foresees they will do
3. God's mercy and grace

I don't know about angels but 1. and 2. are excluded for people (Eph 2:8,9). So any theories about God creating special elect souls or special elect genes are contradicted by scripture. The souls of all people are utterly corrupt at conception and bear the image of Satan. That God has elected some before the foundation of the world is not owning to something within man or due to any foreseen act of man but purely according to His mercy and grace.