The Fab portion of an antibody is formed by portions of both

The F_ab portion of an antibody is formed by portions of both of the heavy chains only. one heavy chain. the variable regions of the light chains. portions of both the heavy and light chains. the light chains only.

Solution

Answer = the Fab portion of antibody is formed by

portions of both heavy & light chain

Fab = is fragment is region on antibody that binds to antigen

It is composed of one constant & one variable domain of each of the constant & heavy chain

The variable domain contains the paratope i.e. antibody binding site