Tutorial to help answer the question:

If a B-cell clone began to produce antibody with altered binding strength and specificity for antigen, you would expect the mutation of the antibody gene to involve:

A.	The variable region of the heavy chain or the constant region of the light chain
B.	The variable region of the light chain or the constant region of the heavy chain
C.	The variable regions of the light or heavy chains
D.	The constant regions of the light or heavy chains

Tutorial

The "variable" region includes 110-130 amino acids of the light and heavy chains, and is responsible for binding to antigen. This part of the antibody shows variations in amino acids when the specificity of the antibody for antigen is changed. The "constant" region is the C-terminal end and contains similar amino acids for each class of antibody. The five major classes of heavy chain are IgM, IgG, IgA, IgD, and IgE.