The simian crease is one of the listed signs in Down Syndrome which would imply there's some genetic factor at play. My eldest daughter has a simian crease on one hand and the other hand is 'normal'.
Sovereign definition, a monarch; a king, queen, or other supreme ruler. See more.
(formal or law) A territory or state, as ruled by a specific power, especially by a king. 1874, Horatio Alger, Brave and Bold, Chapter XXXI, And, of this island realm, he and his companion were the undisputed sovereigns.