Dynamics of Mhc evolution in birds and crocodilians: amplification of class II genes with degenerate primers

Authors

  • S. V. EDWARDS,

    1. Center for Mammalian Genetics and Department of Pathology, University of Florida, Gainesville, FL 32610, USA
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    • *Department of Zoology and Burke Museum, Box 351800, University of Washington, Seattle, WA 98195

  • M. GRAHN,

    1. Center for Mammalian Genetics and Department of Pathology, University of Florida, Gainesville, FL 32610, USA
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    • †Department of Animal Ecology, Ecology Building, S-223 University of Lund, 62 Lund, Sweden

  • W. K. POTTS

    Corresponding author
    1. Center for Mammalian Genetics and Department of Pathology, University of Florida, Gainesville, FL 32610, USA
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‡Tel. +1 (904) 392 6066. Fax: +1 (904) 392 9053. E-mail: potts@cmg.health.ufl.edu

Abstract

Genes of the major histocompatibility complex (Mhc) are the most polymorphic functional loci in mammalian populations, but little is known of Mhc variability in natural populations of nonmammalian vertebrates. To help extend such studies to birds and relatives, we present a pair of degenerate primers that amplify polymorphic segments of one chain (the β chain) of the class II genes from the major histocompatibility complex (Mhc) of archosaurs (birds + crocodilians). The primers target two conserved regions lying within portions of the antigen-binding site (ABS) encoded by the second exon and amplify multiple genes from both genomic DNA and cDNA. The pattern of nucleotide substitution in ABS codons of 51 sequences amplified and cloned from five species of passerine birds and an alligator (Alligator mississippiensis) indicates that archosaurian class II β genes are subject to selective forces similar to those operating in mammalian populations. Hybridization of a genomic clone generated by the primers revealed highly polymorphic bands in a sample of Florida scrub jays (Aphelocoma coerulescens coerulescens). Because the primers amplify only part of the ABS from multiple class II genes, they will be useful primarily for generating species specific clones, thereby providing a critical inroad to more detailed structural and evolutionary studies.

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