The human immunoglobulin heavy chain transgene in the foregoing animals comprises a human constant region gene segment comprising exons encoding the desired heavy chain isotype, operably linked to switch segments from {TAIL ~ a constant region} of {HEAD ~ a different heavy chain isotype}, i.e., a non cognate switch region 
The human immunoglobulin heavy chain transgene in the foregoing animals comprises a human constant region gene segment comprising exons encoding the desired heavy chain isotype , operably linked to switch segments from { TAIL ~ a constant region } of { HEAD ~ a different heavy chain isotype } , i.e. , a non cognate switch region
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