Final answer:
An early pro-B cell must express the variable (V), diversity (D), and joining (J) gene segments to rearrange the immunoglobulin heavy chain genes.
Step-by-step explanation:
For an early pro-B cell to rearrange the immunoglobulin heavy chain genes, it must express the variable (V), diversity (D), and joining (J) gene segments.
During the maturation of the germ-line B cell, an enzyme called DNA recombinase randomly excises V and J segments from the heavy chain gene. Splicing at the mRNA level further rearranges the gene, resulting in a unique variable region capable of binding a different antigen for each antibody.
This genetic rearrangement provides millions of unique antigen-binding sites for the B cell receptor (BCR) and the antibodies secreted after activation.