Bateson and Punnet explained that whentwo dominants enter from the same parent-they try to remain together, called coupling. When two dominantsenter from different parents they try to remain seperatecalled repulsion. Bateson and Punnett (1906) used theterm coupling and repulsion in sweet pea (Lathyrus odoratus) for linkage and crossing over. The correctparental of coupling type along with its cross over or repulsion is coupling AABB, aabb : Repulsion AAbb;aaBB.