Triplication of alpha-globin genes is responsible for unusual alpha 113Leu/alpha 113His-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 the II alpha 113His gene, displaying a reduced efficiency (called the II alpha 113His decreases gene), is carried by a chromosome bearing three alpha-globin loci. In particular, five sheep having an alpha 113Leu/alpha 113His-chain ratio of about 13:1 (13:1 phenotype) possessed the -I alpha 113Leu-II alpha 113Leu-/-I alpha 113Leu-II alpha 113Leu-III alpha 113His decreases genotype. One sheep showing a alpha 113Leu/alpha 113His-chain ratio of about 3:1 (3:1 phenotype) had the -I alpha 113Leu-II alpha 113His-/-I alpha 113Leu-II alpha 113Leu-III alpha 113His decreases genotype, while one sheep having a chain ratio of about 6:1 (6:1 phenotype) carried the -I alpha 113Leu-II alpha 113Leu-II alpha 113His decreases-/-I alpha 113Leu-II alpha 113Leu-III alpha 113His decreases genotype. Nineteen sheep, displaying the common phenotypes, all possessed the alpha alpha/alpha alpha gene arrangement. Furthermore, the possible location of the gene with reduced efficiency and the expression of the three genes in the triple alpha-globin loci chromosome are discussed.