Answer:
The constant region of a heavy chain is the same for all antibodies.
Explanation:
Each heavy chain has two regions, known as the constant region, and the variable region. The constant region is different in antibodies of different isotypes but the same in all antibodies of the same isotype.
The variable region of the heavy chain depending on the white blood cells (B cell) that produced it but is the same for all antibodies produced by a single white blood cell. The variable region of each heavy chain is about 110 amino acids long and is made up of a single Ig domain.