The final section of the 1949 paper discussed genetics. The Caltech authors stated that people suffering from sickle cell anemia were homozygous, whereas people with sickle cell trait were heterozygous. The Longsworth scanning diagrams that they reproduced with their article, definitively show that those with sickle cell trait hemoglobin have two distinct peaks – one that resembles the peak of sickle cell anemia hemoglobin and one that resembles the peak of normal hemoglobin. Thus, they found that sicklemics had one normal allele producing normal hemoglobin and one sickle cell allele producing sickled hemoglobin.

In their discussion on genetics, the authors mentioned that geneticist James V. Neel of the Heredity Clinic at University of Michigan had published a paper earlier that year and proposed the same genetic conclusion. Neel had analyzed the blood of parents and their children and concluded that sickle cell trait is a heterozygous trait, and sickle cell anemia is homozygous recessive. Science published Neel's paper in July 1949, four months before the Caltech paper. Pauling and his collaborators wanted it to be on the record that they reached the same conclusion independently of Neel.

The men at Caltech provided more information about sickle cell anemia than Neel. Their chemical analysis of blood using electrophoresis demonstrated the difference between normal and sickle cell hemoglobin as well as showed sickle cell trait hemoglobin to be a mixture of normal and sickle cell hemoglobins.