Different quantitative expression of the hemoglobin alpha-chain genes in sheep.

We previously reported that the alpha-chain locus of sheep hemoglobin is duplicated and that the II alpha gene is less efficient than the I alpha gene. The II alpha locus controls two allelic alpha chains, one containing leucine (identical to that directed by the I alpha locus) and the other one having histidine in position 113 or 114 (called II alpha 113Leu and II alpha 113His chains, respectively). In sheep homozygous at the II alpha locus for the II alpha 113His allele, the I alpha 113Leu/II alpha 113His-chain ratio was about 1.8:1; in those heterozygous for the II alpha 113Leu and the II alpha 113His alleles, the ratio between the chains was 4-5:1. We report here the detection of a new alpha 113Leu/II alpha 113His-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 alpha D-chain variant. The occurrence of a quantitative polymorphism of the II alpha 113His gene is considered.