Genetically modified mice are provided that express human » variable (hV») sequences. The mice provided include a mouse comprising: (a) an endogenous heavy chain allele comprising an unrearranged human V H , an unrearranged human D H and an unrearranged human J H gene segment； and (b) an endogenous » (lambda) light chain allele comprising an unrearranged human V» and an unrearranged human J» gene segment. The mice provided include mice that express hV» sequences from an endogenous mouse » light chain locus, mice that express hV» sequences from an endogenous mouse º light chain locus, and mice that express hV» sequences from a transgene or an episome wherein the hV» sequence is linked to a mouse constant sequence. Mice are provided that are a source of somatically mutated human » variable sequences useful for making antigen-binding proteins. Compositions and methods for making antigen-binding proteins that comprise human » variable sequences, including human antibodies, are provided.
