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 DH 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.
