Alternative titles; symbols
In apes, Boyer et al. (1973) found evidence for a third alpha locus. The 2 alpha chains of man are identical in amino acid sequence. The same is true for the chimpanzee, gorilla and gibbon. The orangutan alpha chains differ by 1 amino acid. Some persons have 1 alpha locus and rare individuals have 3. Whether those homozygous for 3 loci are at a disadvantage is unclear. Those with 1 locus (a frequent finding in American Blacks) have alpha-thalassemia trait when it is homozygous. Those with 1 gene (out of the usual 4) have Hb H disease. The 2 alpha genes are 3.7 kb apart; the 2 adult globin genes (delta and beta) are 7.0 kb apart. Presumably the closer positioning and other characteristics of the 2 alpha genes allow readier unequal crossingover. The beta and delta genes also have larger introns (intervening sequences) than do the alpha genes. About 0.0036 of American Blacks and 0.05 of Greek Cypriots are heterozygous for 3 alpha loci. In a Welch family, Higgs et al. (1980) found 3 persons with 5 alpha genes.
Boyer, S. H., Noyes, A. N., Boyer, M. L., Marr, K. Hemoglobin 3-alpha chains in apes. J. Biol. Chem. 248: 992-1003, 1973. [PubMed: 4630856]
Higgs, D. R., Old, J. M., Pressley, L., Clegg, J. B., Weatherall, D. J. A novel alpha-globin gene arrangement in man. Nature 284: 632-635, 1980. [PubMed: 6245373] [Full Text: https://doi.org/10.1038/284632a0]
Lie-Injo, L. E., Herrera, A. R., Kan, Y. W. Two types of triplicated alpha-globin loci in humans. Nucleic Acids Res. 9: 3707-3717, 1981. [PubMed: 6269090] [Full Text: https://doi.org/10.1093/nar/9.15.3707]
Trent, R. J., Higgs, D. R., Clegg, J. B., Weatherall, D. J. A new triplicated alpha-globin gene arrangement in man. Brit. J. Haemat. 49: 149-152, 1981. [PubMed: 7272227] [Full Text: https://doi.org/10.1111/j.1365-2141.1981.tb07207.x]