A Explain Briefly How a Vast Number of Immunoglobulins of Different

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A	Explain Briefly How a Vast Number of Immunoglobulins of Different

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The Answer is A. In developing B cells, gene rearrangements within the genetic loci for immunoglobulin light and heavy chains can produce an almost unlimited variety of different variable regions, and thus produce the huge repertoire of antibodies with different specificities for many types of antigen. This gene rearrangement mechanism is called somatic recombination. In the germline configuration, before gene rearrangement, the immunoglobulin loci in progenitor B cells are composed of sequences encoding the constant regions and families of gene segments encoding different portions of the variable region. Heavy-chain loci contain a series of gene segments called variable (V), diversity (D), and joining (J). Light-chain loci contain only V and J gene segments. In somatic recombination in developing B cells, one of each family of gene segments is randomly selected and joined together to give a complete variable-region sequence, which is subsequently expressed as an immunoglobulin heavy or light chain. Immunoglobulin gene rearrangement is irreversible, leading to permanent alteration of the chromosome; it occurs exclusively in B cells.
B. A D gene segment first joins to a J to form DJ, followed by a V becoming joined to DJ to form VDJ, which encodes a complete variable region.
C. The heavy-chain locus rearranges before the light-chain loci. For light chains in humans, the κ locus rearranges first and is followed by the λ locus only if both κ loci fail to produce a successful rearrangement.

A Explain Briefly How a Vast Number of Immunoglobulins of Different

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