A. Nucleotide differences among low polymorphic, high polymorphic MHC class II genes and pseudogenes in the pied flycatcher. Sequences obtained from three different individuals are shown. Motifs allowing the design of loci-specific primers within exon 2 are pointed out with an asterisk. B. Nucleotide variations in the flanking introns of two presumably distinct MHC class II B genes of the woodchat shrike (Lase) and Dupont's Lark (Chde) along with four putatively distinct genes isolated in the white wagtail (Moal). Genes are labelled as DAB1*, DAB2* and so on. Asterisks indicate that the identity of these putative genes is not still confirmed, and future studies may confirm their identity.