Final answer:
A nonproductive V-DJ rearrangement of the heavy-chain locus on the first chromosome would result in an incomplete rearrangement, preventing the production of a functional heavy-chain immunoglobulin molecule. This could be caused by errors in the process of DNA recombination, leading to a loss of diversity in the repertoire of antibodies produced by the B cell.
Step-by-step explanation:
Assuming that an early pro-B cell has productively rearranged D to J segments on both chromosomes, a nonproductive V-DJ rearrangement of the heavy-chain locus on the first chromosome would mean that the V segment did not correctly align and join with the rearranged DJ segments. This would result in an incomplete rearrangement, preventing the production of a functional heavy-chain immunoglobulin molecule. The nonproductive rearrangement could be caused by errors in the process of DNA recombination, such as misalignment or incorrect joining of the gene segments. This would lead to a loss of diversity in the repertoire of antibodies produced by the B cell.