Non-human animals and methods and compositions for making and using them are provided, which non-human animals have a genome comprising an engineered or recombinant diversity cluster within an immunoglobulin heavy chain variable region, which engineered or recombinant diversity cluster comprises an insertion of one or more D<sub>H</sub> segments that are each operably linked to a 23-mer recombination signal sequence. Methods for producing antibodies from non-human animals are also provided, which antibodies optionally contain human variable regions and rodent, e.g., constant regions.
