Final answer:
Lymphocyte precursors are the exception to the rule that differentiated cells do not have permanent DNA sequence changes; they undergo V(D)J recombination to acquire a unique repertoire of antigen receptors.
Step-by-step explanation:
The cell type that is an exception to the rule that the gene expression profile of a differentiated cell does not involve permanent changes to the DNA sequence is C Lymphocyte precursors. During the development of lymphocytes, specifically in the process of creating B and T cells, gene rearrangement occurs. This process, known as V(D)J recombination, involves permanent changes to the DNA sequence in order to generate a vast array of antigen receptor specificities. Thus, this is a case where the differences between cells of the same organism are due to actual changes in the DNA sequence, rather than merely differential gene expression.
While all somatic cells generally contain the exact same genome and express different sets of genes to become specialized, lymphocyte precursors undergo a unique process. They rearrange their DNA sequences to produce a diverse repertoire of immune responses. It is through this process that lymphocytes are equipped with the means to recognize and respond to a vast array of pathogens. Such changes are heritable in the sense that once a lymphocyte has rearranged its DNA to create a unique receptor, all its progeny will inherit this rearranged sequence.