Genetic variation at the DNA level between seven sheep breeds : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Applied Science at Lincoln University

Abstract

To assess genetic variation at the DNA level within the sheep population, 4 domestic and 3 exotic breeds were selected and DNA extracted from 10 unrelated individuals from each breed. Sixteen DNA probes were used to assess allele frequency differences between the breeds at known polymorphic loci, and to search for new polymorphisms at · specific loci.

Using 'multi-gene' probes, no polymorphisms were identified that were suitable for scoring differences in allele frequency between the breeds. However, significant variation was observed between Romney related breeds (Coopworths, Perendales) and Merinos at several known polymorphic loci. At the haemoglobin locus, a probe which appears to detect alleles coding for HbA and/or HbB as classified by protein electrophoresis, failed to detect haemoglobin alleles in all samples. This suggests the presence of a putative third allele detected by RFLP analysis but not routine starch gel electrophoresis. This allele appeared predominant in the Texels, but was also observed in the Romneys, Coopworths and Merinos.

Three loci previously characterised in Romneys and Merinos only, were rescreened in Coopworths and the exotic Gotland, Finn and Texel breeds to look for new polymorphisms. The Texels appeared to have an insertion/deletion polymorphism around the ~-FSH locus which was different to the insertion/deletion previously reported (Montgomery et al. 1990b). A third polymorphism at the ~-FSH loci, showed similar allele frequencies in Gotlands and Finns which were different to those observed in the other breeds.

Differences observed suggest a high level of genetic variability between unrelated sheep breeds. Similarity of allele frequencies between the Gotlands and Finns at many loci suggests that these two breeds may be related. Romneys, Coopworths and Perendales appear similar at all loci, while Texels and Merinos do not appear to be closely related to any of the breeds studied.