Mice having a restricted immunoglobulin heavy chain locus are provided, wherein the locus is characterized by a single polymorphic human V H gene segment, a plurality of human D H gene segments and a plurality of J H gene segments. Methods for making antibody sequences that bind an antigen ( e.g ., a viral antigen) are provided, comprising immunizing a mouse with an antigen of interest, wherein the mouse comprises a single human V H gene segment, a plurality of human D H gene segments and a plurality of J H gene segments, at the endogenous immunoglobulin heavy chain locus.
