9] ABNORMAL HUMAN HAEMOGLOBINS 151 



Genetic evidence shows that the haemoglobin S and the haemoglobin C 

 mutations may be allelic,^' i.e. that they occur in the same locus. We can now 

 give a chemical interpretation of this statement, not in terms of the chemical 

 constitution of the gene but of the amino acid sequence of the polypeptide 

 chain whose synthesis the gene controls. In the two mutations discussed in 

 this paper the same very small portion of the haemoglobin gene seems to 

 be affected and in turn the identical amino acid in the polypeptide chain is 

 replaced by either valine or lysine in haemoglobin S and C respectively. 

 The two mutations are indeed alleles. 



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