Frequency of clonal expansion in different B-cell populations. Large clonal expansions were observed in antigen-experienced memory populations. Sequencing of Ig gene rearrangements showed that some occurred more than once, and were considered to belong to a clonal family. Members of the same clone (with the same junctional CDR3 sequence) were identified. The size of each family was noted but only 1 member of each family was used in subsequent analyses. We plotted the frequency distribution of sequences between clones of different size for transitional (IgD⁺CD27⁻CD10⁺, n = 433), naive (IgD⁺CD27⁻CD10⁻, n = 662), switched memory (IgD⁻ and either IgG⁺ or IgA⁺, n = 1293) and IgM memory (IgD⁺CD27⁺, n = 1209) populations. Clone size of 1 indicates no related sequences were found.