<prompt> Isoantigens are -Found in some but not all members of speciesFound in some but not all members of speciesOccurs in different biological species, class and kingdomsAll individuals in a paicular species  <response>: Isoantigens are antigens found in some but not all members of a species. A species may be grouped depending on the presence of different isoantigens in its members. The best example is human erythrocyte antigens, based on which individuals can be classified into different blood groups. Reference:athanarayan panikers 9th edition, pg no: 89 p 