Fig. 1

Schematic of D region clusters at the Bos taurus immunoglobulin heavy chain locus. a D-region cluster 2, comprising an ultralong IGHD, is shorter than highly homologous clusters. The DH regions are organized in four clusters at the immunoglobulin heavy chain locus on Bos taurus chromosome 21. Three clusters are homologous (clusters 2, 3 and 4 which are boxed). Green rectangles represent DH regions; orange, JH regions; light orange, pseudogene JH regions; blue, CH regions; light blue, pseudogene CH regions; and light pink, pseudogene VH regions. A red triangle indicates the position of the ultralong IGHD8–2. The entire locus is not shown; VH regions are upstream and remaining constant regions are downstream of the region shown. b Cluster 2 has a deletion and rearrangement in relation to clusters 3 and 4. Aligned schematic of the DH regions and their locations within the clusters. The numbers inside the boxes indicate the family members of each DH (e.g. on the first line, “1” represents IGHD1–2, and “1” on the second line represents IGHD1–3, etc.). IGHD5 is labeled in red to illustrate its unusual location in cluster 2 relative to clusters 3 and 4. The ultralong DH, IGHD8–2, is outlined in green, and indicated by a red triangle above. The transparent grey box encompassing IGHD3 and IGHD7 regions represents the approximate region of a large nucleotide deletion in cluster 2 relative to clusters 3 and 4. Open triangles represent the recombination signal sequences (RSS) containing heptamer, 12 basepair spacer, and nonamer regions