1. Three generations of a family of Italian descent were studied. Nine of 13 members were found to have thalassemia minor.
2. Genetic studies indicate that this mild, microcytic hypochromic anemia characterized by the presence of target and elliptical cells and other bizarre forms and by increased resistance to hypotonic saline, results from heterozygosity of an inherited factor, which, when homozygous, produces thalassemia major or Cooley’s Mediterranean anemia.
3. If individuals heterozygous for this factor (thalassemia minor) marry other heterozygous individuals, one quarter of the offspring can be expected to be homozygous (thalassemia major), one half heterozygous (thalassemia minor) and one quarter free of the trait.
4. The presence of thalassemia minor apparently did not interfere with the general health of affected members of this family and did not appear to shorten life expectancy. The importance of the condition lies in its relation to thalassemia major.