Final answer:
The kappa and lambda light genes are not located on the same chromosomes, can associate with all types of heavy chains, and are not both expressed by the same B cell; therefore, the correct answer is D) None of the above.
Step-by-step explanation:
The question concerns the characteristics of kappa (k) and lambda (λ) light genes in B cells. The correct choice from the options provided is D) None of the above. Here's why:
- Kappa and lambda light genes are located on different chromosomes, kappa on chromosome 2 and lambda on chromosome 22.
- Both types of light chains, kappa and lambda, can associate with any type of heavy chain, forming different types of immunoglobulins (IgG, IgA, IgM, IgE, IgD).
- A single B cell expresses either kappa or lambda light chains, but not both simultaneously. Once a B cell has successfully produced a functional light chain, it will continue to produce that specific type of light chain exclusively.
These light chains are crucial for the diversity of antibodies. Complex genetic recombination involving V (variable), J (joining), and sometimes D (diversity) segments leads to the vast repertoire of antibodies, each with unique antigen-binding sites. Although the constant domain of light chains does not bind to antigens, it plays a role in the structural integrity and functional location of the antibody.
The process of genetic recombination ensures that every B cell has a unique specificity to an antigen, thus preparing the immune system to respond to a multitude of pathogens efficiently. The kappa to lambda ratio in humans is approximately 2:1, with 65% being kappa light chains and 35% being lambda.