Fig. 4

Expansion of MHCIIB and DMB genes in duck. a,b Maximum likelihood trees of MHCIIB (a) and DMB genes (b). Amphibian MHCIIB (classical MHCII β chain) and DMB (non-classical MHCII β chain) genes were set as outgroup. Numbers of the tree branches are bootstrap percentages with 1000 iterations. Abbreviated information on species is in Additional file 1: Table S20. c Expression of MHCII and DM genes in eight duck tissues. The MHCII heterodimer has two chains, namely MHCIIα (encoded by MHCIIA) and MHCIIβ (encoded by MHCIIB). The DM heterodimer consists of two chains, namely DMα (encoded by DMA) and DMβ (encoded by DMB). Detailed sample information is in Additional file 3: Data S6. d Multiple sequence alignment and domain of duck MHCIIβ proteins. “-” denotes gap, and “·” indicates the same amino acid as the first reference sequence. e Schematic of 14 DMβ2 proteins