P. A. Swarbrick

CLONING AND SEQUENCING OF EXPRESSED DRB GENES OF THE RED DEER (CERVUS ELAPHUS) MHC

The expressed major histocompatibility complex (Mhc) class II DRB genes of 50 unrelated deer were examined by reverse transcription polymerase chain reaction, cloning, and sequencing of DRB exon 2. Deer, like other mammals, have at least one highly polymorphic Mhc class II DRB gene. Thirty-four different sequences were identified. Most of the variation in amino acid composition occurred at positions that have been shown to form the peptide binding site (PBS). Eighteen deer-specific substitutions were found, 11 of these occurred in the PBS. Significantly higher rates of replacement substitutions than silent substitutions were found in the deer sequences, indicating strong positive selection pressure for diversity in DRB sequences. Between one and four DRB sequences were found per deer. Inheritance of these sequences in pedigrees showed Mendelian segregation with up to two expressed DRB genes per haplotype. Sheep are the only other ruminant in which the presence of more than one expressed DRB gene has been demonstrated. Phylogenetic trees were constructed in an attempt to assign the deer DRB sequences to specific loci, but no clear segregation of the DRB sequences for different loci was found. It would seem likely that sequence exchange between the loci has occurred. As has been shown in other species, the α-helix and β-sheet regions of exon 2 appeared to have different evolutionary histories.

MAF45, a highly polymorphic marker for the pseudoautosomal region of the sheep genome, is not linked to the fecXI (Inverdale) gene

A highly polymorphic dinucleotide repeat, or microsatellite, that shows partial sex-linked inheritance in sheep has been isolated from the sheep genome. Our data indicate that the locus is in the pseudoautosomal region approximately 13 cm from the boundary with the sex-linked regions. The locus, designated MAF45, has 12 alleles with a PIC of 0.84. The same primers amplify a single polymorphic locus in cattle and goats. This locus was not linked to the Inverdale gene, an X-linked gene that increases the ovulation rate in sheep.

DNA fingerprinting analysis of Booroola pedigrees: a search for linkage to the Booroola gene.

Seven minisatellite probes from a variety of sources were used to analyse 11 paternal half-sib families in which the Booroola gene was segregating. A total of 402 bands that showed segregation in the pedigrees were examined for linkage to the Booroola gene. None of the bands showed segregation with the Booroola gene. The most likely evidence for a linked band was produced by the HaRas HVR probe in Family 902 (θ=0.0; LOD 2.3). The conclusion, however, is that the minisatellite probes used in this study could not be used as markers for the Booroola gene. The study highlighted problems associated with the use of minisatellite probes in linkage studies in half-sib families. The complex banding patterns found on fingerprinting gels was a major source of scoring error. In a few cases both of the sires alleles could be identified at a particular locus, but in most cases only one of the alleles could be identified. For the most part, the bands had to be treated as dominant alleles. The contribution of dam alleles to the banding pattern could only be estimated. There was an indication that minisatellite loci in sheep are clustered in particular regions of the sheep genome as the rate at which bands segregated with each other was higher than one would expect from loci randomly distributed throughout the genome.