Compositions and methods are disclosed for generating immunoglobulin structural diversity in vitro, and in particular, for reducing biases in V region and J segment gene utilization, and for generating immunoglobulin V-D-J recombination events in a manner that does not require D-J recombination to precede V-DJ recombination. Selection of advantageous combinations of immunoglobulin gene elements, including introduction of artificial diversity (D) segment genes and optimization of recombination signal sequence (RSS) efficiency, are disclosed.