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