Gene Action and Polypeptides 



415 



mutants are on the same chromosome. In 

 fact, the simplest explanation is that the fl x 

 chain is specified by a single gene whose 

 various mutants cause the different single 

 amino-acid substitutions mentioned. 



Still other kinds of adult hemoglobin A 

 are found. In some cases the amino acid 

 sequence in the a chain is modified, as in 

 hemoglobin I (in which a change occurs in 

 position 16) and in hemoglobin "Hopkins- 

 2." Since an adult homozygous for hemo- 

 globin A has a molecule describable as 



<r;}[3}, an individual homozygous for the gene 

 for sickling can have its hemoglobin de- 

 scribed as agjSfj an d one homozygous for 

 the production of hemoglobin I can have 

 its molecule written a!,(i.}. A list of some of 

 the genetically-determined chemical variants 

 of Hb-A is given in Figure 32-7. In each 

 case a single amino acid replacement is in- 

 volved. 



The biochemical genetics of Hb-A 

 strongly supports the view that the synthesis 

 of the nonenzymatic protein globin is a pri- 



figure 32-7. Genetically determined variants of Hb-A. 



Hb Type 



Amino Acid Position 



Change Involved 



P 



Chain 



s 

 c 



San Jose 

 E 



Saskatoon 

 Zurich 



M 



Milwaukee -1 



Arabia 



6 

 6 



7 



26 

 63 

 63 

 67 

 121 

 121 



Glu ►- Vol 



Glu ► Lys 



Glu ► Gly 



Glu >- Lys 



His ► Tyr 



His ► Arg 



Vol ► Glu 



Glu ► Lys 



Glu +- Glu-NHj 



16 

 30 

 57 

 58 

 68 

 116 



Lys ► Asp 



Glu >~ Glu-NH, 



Gly >- Asp 



His +- Tyr 



Asp-NHj P- Lys 



Glu ► Lys 



