IX. GENETICS AND HUMAN HEMOGLOBIN CHEMISTRY 



443 



somewhat slower than that of Hb-D; this hemoglobin was found to be 

 alkali-resistant and to have the same N-terminal amino acids as Hb-F. 

 One of the parents of each baby was heterozygous for Hb-Dst. Louis. Min- 

 nich et al. (1962) postulated that the abnormal fetal hemoglobin resulted 

 from the combination of a^st.Louis chains with y'" chains. Similar cases 

 have been observed by Weatherall and Boyer (1962). The cord blood 

 hemoglobins of a Negro baby have been studied by Weatherall and 

 Baglioni (1962); column chromatography on IRC-50, according to 

 Allen et al. (1958), showed the presence of four hemoglobins, identified 

 by fingerprinting as Hb-F, Hb-F/Gphnadeiphia Hb-A, and Hb-Gpunadeiphia 

 in the order of elution from the column. The alteration of Hb-Gphiiadeiphia 

 is known to reside in the a peptide chain (Baglioni and Ingram, 1961). 

 These results show that the a chain of Hb-A and Hb-F are under the 

 control of the same a gene. The a peptide chains of Hb-A and Hb-F have 

 been shown to be chemically indistinguishable (Hunt, 1959; Schroeder 

 et al., 1961). Nomial ao^ dimers and abnormal a^^ dimers are produced in 



Fig. 10. Schematic explanation of the presence of four hemoglobins in fetuses or 

 newborns heterozygous for an a chain mutation (Minnich et al., 1962; Weatherall 

 and Boyer, 1962). The loci controlling the synthesis of a, /3, and y peptide chains are 

 represented on the left. The arrows show the different dimers synthesized under the 

 control of the two a alleles and of the /3 and y genes. These dimers combine 

 randomly in the last stage of assembly of the hemoglobin molecule to form the four 

 hemoglobins indicated by capital letters. 



