Final answer:
The correct statement about somatic recombination is that the heavy chain undergoes rearrangement before the light chain. Somatic recombination pertains to the variable, diversity, and joining (V, D, J) gene segments which provide the necessary diversity for antibody production in B cells.
Step-by-step explanation:
The question asks to identify the true statement among the given options about somatic recombination, which is a biological process occurring in B cells that leads to the generation of antibody diversity. Let's evaluate each statement:
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- a. The heavy chain is observed to undergo rearrangement before the light chain. This statement is true. During B cell development, the heavy chain locus rearranges first. If this is successful, the light chain locus will rearrange.
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- b. Rearrangement of genes will occur within the constant domain of the antibody. This statement is false. Gene rearrangement occurs in the variable (V), diversity (D), and joining (J) segments, not in the constant (C) domain of antibodies.
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- c. To rearrange and combine V, D, & J genes segments, AID must be used. This statement is false. AID (Activation-Induced cytidine Deaminase) is involved in somatic hypermutation and class-switch recombination, not V(D)J recombination.
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- d. The 1/2 -turn rule ensures TLR gene segments are aligned in the correct order. This statement is false. The 1/2-turn rule does not apply to B cell receptor (BCR) or T cell receptor (TCR) gene segment rearrangement; it is related to DNA structure.
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- e. CDR1 & CDR2 encoding for the L-chain is accomplished via different D gene segments. This statement is false. There are no D segments in light chain rearrangement; only variable (V) and joining (J) segments are involved.
Therefore, the correct statement about somatic recombination is the first one, (a) The heavy chain is observed to undergo rearrangement before the light chain.