Triplication of α-globin genes is responsible for unusual α113Leu/α113His-globin chain ratios in sheep

By investigations at the DNA and protein level, it has been shown that in sheep a previously detected, presumed quantitative allele of theIIα113His gene, displaying a reduced efficiency (called theIIα113His↓ gene), is carried by a chromosome bearing three α-globin loci. In particular, five sheep having an α113Leu/α113His-chain ratio of about 13:1 (13:1 phenotype) possessed the —Iα113Leu—IIα113Leu—/—Iα113Leu—IIα113Leu —IIIα113His↓ genotype. One sheep showing a α113Leu/α113His-chain ratio of about 3:1 (3:1 phenotype) had the —Iα113Leu—IIα113His—/—Iα113Leu—IIα113Leu —IIIα113His↓ genotype, while one sheep having a chain ratio of about 6:1 (6:1 phenotype) carried the —Iα113Leu—IIα113Leu—IIα113His↓—/—Iα113Leu—IIα113Leu —IIIα113His↓ genotype. Nineteen sheep, displaying the common phenotypes, all possessed the αα/αα gene arrangement. Furthermore, the possible location of the gene with reduced efficiency and the expression of the three genes in the triple α-globin loci chromosome are discussed.