Sequence Variation At The Major Histocompatibility Complex Locus DQB In Finless Porpoise (Neophocaena Phocaenoides)

Genetic variation at exon 2 (including part of the putative peptide-binding region, PBR) of the class II major histocompatibility complex (MHC) DQB locus was analyzed in 195 finless porpoises (Neophocaena phocaenoides) from three populations in Chinese waters, i.e. the Yangtze River population, the Yellow Sea population, and the South China Sea population. Exon 2 of DQB locus was amplified via the polymerase chain reaction, followed by single-stranded conformation polymorphism analysis, cloning, and then sequencing. Among the 172bp nucleotide sequences of 200 clones, 19 variable sites were determined and 11 alleles were identified. All the 11 alleles show no insertion / deletion, or stop codons, and therefore could be assumed functional in vivo. Pairwise comparisons of these alleles showed a 4.101:1 ratio of non-synonymous to synonymous substitutions per site (dn/ds) leading to 16 amino acid differences, eight of which were at putative PBR sites. This indicated that DQB locus played an important role in cellular response. Different with the marine mammals but like the baiji, the finless porpoises showd relatively high level of MHC diversity.Convergent evolution is the emergence of biological structures or species that exhibit similar function and appearance but that evolved through widely divergent evolutionary pathways. The similarities that are shared in case of convergent evolution are not the result of evolution from a common ancestor sharing those...