The 'gene type' concept allows to identify the genes present in the immunoglobulin or T cell receptor sequences.
There are four instances of the 'gene type' concept: the variable (V), diversity (D) and joining (J) genes which
encode the antigen binding sites, and the constant (C) genes which encode the part of the protein which has effector properties.
The 'gene type' concept is part of the 'IDENTIFICATION' concept of IMGT-ONTOLOGY 
 Giudicelli, V. and Lefranc, M.-P., Bioinformatics, 15, 1047-1054 (1999)