Glucosephosphate isomerase polymorphism in sheep.

Two types of glucosephosphate isomerase (GPI) are described for the first time in sheep. Type T produced a 3-band pattern on polyacrylamide gel electrophoresis of serum samples, whereas type M produced a pattern of 5-7 bands. When 23 Scottish Halfbred ewes showing type T were mated to 3 Suffolk rams showing type M, their 32 offspring had frequencies of 0.72 and 0.28 for T and M respectively. There was no conclusive evidence that the types were controlled by codominant alleles or by simple Mendelian inheritance and neither was sex-linked. The frequency of the rarer type (M) was sufficiently high to provide conclusive evidence of true enzyme polymorphism.