Merinos (189) and Poll Dorsets (106) were compared for genetic variation at 30 loci for blood proteins. ‘Malic enzyme’ and NADH diaphorase I polymorphism occur in Merinos but not in Poll Dorsets, whereas both breeds are polymorphic for haemoglobin, erythrocyte X-protein, serum esterase, catalase and transferrin, although the breeds differ in the presence or absence of certain rare transferrin variants. Poll Dorsets but not Merinos have genetic variation of erythrocyte pyruvate kinase at low gene frequencies; Merinos but not Poll Dorsets have genetic variation of two erythrocyte Gly-Leu peptidases, glucosephosphate isomerase, superoxide dismutase, and NADH diaphorase II, all at low gene frequencies (P < 0·05).
Using Masatoshi Nei's (1972, 1976) standard genetic distance, over all 30 loci, to calculate the time of divergence of the two breeds, we obtained t = 69700 years – whereas sheep are believed to have been domesticated by man for not more than 11000 years, and ancestors of the British breeds and of the Merino have probably not been separated for more than 2000 years. Several possible explanations for this discrepancy are discussed, including the accuracy of the coefficient of codon change (α), changes in population size and structure, selection, and additional hybridization in the ancestry of the Merino.