Amino acids use is reported as the percent of the sequenced population from neonatal liver Fraction F (NL F - mature); peritoneal cavity (PerC) B-1a, B-1b and B-2; and bone marrow fraction F (BM F - mature, recirculating) from either wild type or TdT−/− mice (BM F TdT−/−). The amino acids are arranged by relative hydrophobicity, as assessed by a normalized Kyte-Doolittle scale (39, 40). The number of loops analyzed is shown. (top) all VH7183 transcripts; (middle) VH7183 transcripts from PerC B cells CDR-H3 without N nucleotide addition (N−); (bottom) VH7183 transcripts from PerC B cell CDR-H3 containing N nucleotide addition (N+). All comparisons were made to fraction F, either from 1 day liver (NL F) or bone marrow (BM F) using χ2-test or Fisher’s exact test as appropriate. Significant differences between PerC B cell subsets and both fraction Fs are labelled with asterisks, with *p≤0.05, **p≤0.01, *** p≤0.001, **** p≤0.0001.