Horse serum esterase: Investigations on the relationship between qualitative and quantitative expression of allelic genes

The esterase in the blood serum samples of horse populations was estimated both to detect the null allele and to evaluate individual variability. Quantitative assays carried out on 800 sera classed by electrophoretic phenotypes and irrespective of family relationship, breed, sex, or age, showed marked individual variation of esterase activity. However, no differential activities for the four allelic variants examined could be demonstrated. Very low esterase activities were considered to be an indication of the presence of the null allele; in the majority of cases this hypothesis was confirmed by immunochemical titration of esterase protein and examination of family relationships. Conversely, in a limited group of closely related horses the presence of the null allele was easily inferred from examination of genealogies and phenotype comparison; it was further confirmed by immunochemical titration.