Question

21. Which of the following accounts for allelic exclusion in rearrangement within the IgH locus?

A. Rearrangement only occurs on one homolog at a time, and once one homolog has successfully rearranged, the other is methylated to produce heterochromatin.
B. Rearrangement is regulated by VpreB and λ5, which are themselves only expressed at specific times during IgH rearrangement.
C. Both homologs rearrange simultaneously, undergoing multiple V-J rearrangements until a productive one occurs.
D. All of the above promote allelic exclusion in IgH.
E. Allelic exclusion does not occur in IgH.

Answer 1

Allelic exclusion within the IgH locus is accounted for by the process in which only one allele rearranges at a time; successful rearrangement leads to methylation and heterochromatin formation in the other allele, contributing to the creation of a unique antigen receptor for each B cell.

Step-by-step explanation:

The account for allelic exclusion in rearrangement within the IgH locus is that rearrangement occurs only on one homolog at a time, and once one homolog has successfully rearranged, the other is methylated to produce heterochromatin. This process ensures that each B cell expresses a unique antigen receptor, which is crucial for the diversity and specificity of the immune response. Genetic rearrangement involves the joining of V (Variable), D (Diversity), and J (Joining) segments for the heavy chain, and V and J segments for the light chain, which together contribute to a huge variety of antigen-binding sites in antibodies.