There are millions of antigens that the body comes across daily. All these antigens are recognized specifically by the antibodies due to their variable region. This diversification in antibody production is called as antibody diversity.
Antibody diversity is generated by multiple mechanisms, each of which contributes to the generation of antibodies with up to 1011 different amino acid sequences in their antigen-binding sites. Several of these mechanisms involve changes in the DNA sequences encoding the antibody heavy and light chain proteins. One mechanism that does not rely on changes to the DNA within the immunoglobulin heavy and light chain gene loci is instead dependent on the activity of terminal deoxynucleotidyl transferase (TdT) to add random nucleotides at the junctions between the V, J, and D region sequences.
So, the correct answer is (4) The activity of TdT to add random nucleotides at the junctions between the V, J, and D region sequences.
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