Genetically modified non-human animals with humanized immunoglobulin locus

A genetically-modified rodent comprising at an endogenous heavy chain immunoglobulin gene locus human Immunoglobulin Heavy Variable (IGHV) genes, human Immunoglobulin Heavy Diversity (IGHD) genes, and human Immunoglobulin Heavy Joining (IGHJ) genes at the heavy chain immunoglobulin gene locus of human chromosome 14 from a human cell, wherein the human IGHV genes, the human IGHD genes, and the human IGHJ genes are operably linked and can undergo VDJ rearrangement, wherein a contiguous human sequence is integrated into the endogenous chromosome by recombination, and the human sequence is at least 500 kb, wherein the modification can be detected by PCR using one or more primer pairs selected from the group consisting of:

• (a) SEQ ID NO:
• 13 and SEQ ID NO:
• 14;
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• 15 and SEQ ID NO:
• 16;
• (c) SEQ ID NO:
• 17 and SEQ ID NO:
• 18;
• (d) SEQ ID NO:
• 19 and SEQ ID NO:
• 20;
• (e) SEQ ID NO:
• 21 and SEQ ID NO:
• 22;
• (f) SEQ ID NO:
• 23 and SEQ ID NO:
• 24;
• and
• (g) SEQ ID NO:
• 25 and SEQ ID NO:
• 26.