The T-cell receptor (TCR) subunits (α, β, γ, δ) are encoded by genes located at different positions in the human genome. Allelic exclusion during T cell development ensures that a T cell can only express either αβ or γδ TCR, but not both simultaneously. This mechanism prevents mispairing of TCR subunits.

The immunoglobulin heavy chain gene consists of V, D, J, and C regions, allowing for class switching. In contrast, the light chain gene lacks D segments and class switching capability. Both use V(D)J recombination and somatic hypermutation. The heavy chain locus is more complex, enabling class switching between different isotypes, while the light chain locus is simpler.

The development of B cells involves several key genetic processes. V(D)J recombination rearranges gene segments to produce the BCR, V(D)J selection tests its functionality, and class switching allows switching between IgM, IgG, IgA, or IgE isotypes. Somatic hypermutation introduces point mutations, increasing BCR affinity. AID is crucial for these processes.