The invention provides improved non-human vertebrates and non-vertebrate cells capable of expressing antibodies, eg, comprising human variable region sequences. The invention provides for enhanced AID and/or AID homologue spectra, thereby providing for the increased diversity as a result of somatic hypermutation and/or class-switch recombination during in vivo antibody generation. The invention also provides methods of generating antibodies using such vertebrates, as well as the antibodies per se, therapeutic compositions thereof and uses.
