The zeta chain is an alpha-type chain of mammalian embryonic hemoglobin. Heterotetramer of two zeta chains and two epsilon chains in early embryonic hemoglobin Gower-1; two zeta chains and two gamma chains in fetal hemoglobin Portland-1. Heterotetramer of two zeta chains and two beta chains in hemoglobin Portland-2, detected in fetuses and neonates with homozygous alpha-thalassemia. Detected in fetal erythrocytes (at protein level). Detected in the yolk sac of the early embryo and in erythrocytes from fetal umbilical cord blood. Detected at low levels after 10 weeks of gestation. Hemoglobin Portland levels are increased in fetuses with homozygous alpha-thalassemia, but it constitutes only a minor proportion of total hemoglobin and its levels decrease steadily after 10 weeks of gestation. Hemoglobin Portland-2 is detected in blood from still-born neoneates with homozygous alpha-thalassemia (at protein level). Belongs to the globin family.