Genetic events that lead to diversification of SH2 families.(A) Diagram representing the events of domain gain or loss either prior to or after events of gene duplication. (B) Classification of SH2 families on the basis of genome duplication events and domain loss or gain. Class 0, represented by the RASA1 family, do not undergo gene duplication. Class IA, represented by the SRC family, undergoes events of complete gene duplication without domain loss or gain. Class 1B, represented by the SLP76 family, diversify by acquiring new domains and undergoing gene duplication. Class IC, represented by the CBL family, undergoes gene duplication with domain loss.Class II, represented by the SLAP family, undergoes domain loss followed by gene duplication.