The genetic organisation of the ovine DQB region: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Science with Honours at Lincoln University

Abstract

The major histocompatibility complex (MHC) is a multi-gene family which plays a central role in mediating a number of immunological functions related to acquired immunity. The ovine MHC consists of several defined regions including the highly polymorphic DQ region. This region consists of DQA and DQB genes with the DQA region typically consisting of two loci, DQAJ and DQA2, although the DQAJ gene is absent in approximately twenty percent of sheep. It has been proposed that DQB also consists of two loci and that these loci are tandemly arranged with the DQA genes, but this has never been confirmed. Twenty-five unique DNA sequences have been identified as most likely being alleles of the ovine DQB gene, but it is unclear as to whether these sequences have been derived from more than one DQB locus as conflict occurs in the current literature. Polymerase Chain Reaction (PCR) was used to amplify exon 2 of the ovine DQB gene. It was observed that a single DQB sequence was obtained from sheep that were DQAJ null heterozygotes (i.e. have one DQAJ locus). In contrast for sheep homozygous for DQAJ null, no DQB amplimer was obtained. This suggests the presence of two DQB loci and an association between the DQA and DQB genes.