Final answer:
Step 3 of the RAG1/2 and HMG mediated V(D)J rearrangement involves the joining of the V, D, and J gene segments into a unique variable region by an enzyme called DNA recombinase, generating diverse antibodies for immune response.
Step-by-step explanation:
The question asks about step 3 of the RAG1/2 and HMG mediated V(D)J rearrangement. This process occurs during the development of the immune system, particularly for B and T lymphocytes. V(D)J recombination is the mechanism of rearranging the variable (V), diversity (D), and joining (J) segments of immunoglobulin genes to create a diverse repertoire of antibodies.
In the context of V(D)J recombination, step 3 usually refers to the joining of these gene segments. An enzyme called DNA recombinase excises most of the segments from the gene and splices one V segment to one J segment. In the case of the heavy chain, a D segment is also included. This recombination generates a unique variable region capable of binding a different antigen. The enzyme RAG1 is closely related to genes in a family of transposons and plays a critical role in mediating this recombination.