Final answer:
The variability hot spots in the immunoglobulin light and heavy chains' variable regions are known as complementarity determining regions (CDRs), critical for antigen binding and antibody diversity.
Step-by-step explanation:
The hot spots of variability inside the variable regions of the light and heavy chains of immunoglobulins are called complementarity determining regions (CDRs). These regions show marked variability in amino acid sequence composition and are essential for the formation of the antigen-binding site. The variable regions of both the light and heavy chains of an antibody, which include the hypervariable regions, interact to form a binding site for a specific epitope on an antigen. The presence of these hypervariable regions allows for the generation of a diverse range of antibodies capable of binding to a vast array of antigens. This diversity is crucial for the immune system's ability to recognize and respond to a wide variety of pathogens.