Different quantitative expression of the hemoglobin α-chain genes in sheep

We previously reported that the α-chain locus of sheep hemoglobin is duplicated and that the IIα gene is less efficient than the Iα gene. The IIα locus controls two allelic α chains, one containing leucine (identical to that directed by the Iα locus) and the other one having histidine in position 113 or 114 (called IIα113Leu and IIα113His chains, respectively). In sheep homozygous at the IIα locus for the IIα113His allele, the Iα113Leu/IIα113His-chain ratio was about 1.8:1; in those heterozygous for the IIα113Leu and the IIα113His alleles, the ratio between the chains was 4–5:1. We report here the detection of a new α113Leu/IIα113His-chain ratio of 12–15:1, observed in 16 sheep belonging to four domestic breeds, during a survey of 245 animals. This phenotype was found associated in five sheep with the αD-chain variant. The occurrence of a quantitative polymorphism of the IIα113His gene is considered.