(a) IGLV and (b) IGLJ gene segments were studied in the fetal liver (light gray), fetal bone marrow (dark gray), and adult horse bone marrow (black). The quantity of unique sequences utilizing each gene segment is shown. Significant differences (p-values ≤ 0.0001**) between the two most common IGLV segments (IGLV4-66, IGLV8-128) were observed with the Fisher’s Exact Test between fetal liver and adult horse bone marrow, fetal bone marrow and adult horse bone marrow, and all fetal and adult horse bone marrow; fetal liver and fetal bone marrow were not significantly different (p-value = 1.0). Significant differences (p-values ≤ 0.01*) were also observed for the two most common IGLJ (IGLJ5, IGLJ7) segments between fetal liver and adult horse bone marrow, fetal bone marrow and adult horse bone marrow, and all fetal and adult horse bone marrow; fetal liver and fetal bone marrow gene segment usages were not significantly different (p-value = 0.7).